Effective April 16, 2026, the Postal Service™ is revising Publication 52, Hazardous, Restricted, and Perishable Mail, in various sections, to reflect an update in Postal Service mail class availability, packaging, marking and labeling requirements for certain mailable dangerous goods in the Postal Service international mailstream. These changes reflect recent updates to the Universal Postal Union Regulations to the Convention, Final Protocol (2025).
Although these revisions will not be published in Publication 52 until later, these standards are effective immediately.
Publication 52, Hazardous, Restricted, and Perishable Mail
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3 Hazardous Materials
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34 Mailability by Hazard Class
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346 Toxic Substances and Infectious Substances (Hazard Class 6)
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346.3 Division 6.2, Infectious Substances Mailability
346.31 General
[Revise the text of 346.31 to read as follows:]
The following apply:
a. Conditions for mailing Division 6.2 infectious substances:
(1) International Mail: Category A infectious substances are nonmailable. Category B infectious substances (as defined in 346.12(a)2) are permitted when they are intended for medical or veterinary use, research, or laboratory certification related to public health, and are properly prepared for mailing. The mailer must receive written approval from the director, Product Classification. (Refer to 214 for contact information.) See 622.2 and Mailing Standards of the United States Postal Service, International Mail Manual (IMM), section 135, for specific requirements.
(2) Domestic Mail: Infectious substances are mailable only when intended for medical or veterinary use, research, or laboratory certification related to public health, and must be properly prepared to withstand shocks, pressure changes, and other conditions incident to ordinary handling in transit. The following substances are mailable subject to the corresponding packaging requirements:
(a) Category B Infectious Substance: Packaging Instruction 6C.
(b) Sharps and Other Mailable Regulated Medical Waste: Packaging Instruction 6D.
(c) Used Health Care Products: Packaging Instruction 6E.
(d) Forensic Materials: Packaging Instruction 6F.
(e) Nonregulated Materials: Packaging Instruction 6G.
(f) Exempt Human or Animal Specimens: Packaging Instruction 6H.
b. Special conditions: The following items are permitted to be mailed within specific quantity limits and packaging conditions specified in 346.3:
(1) Infectious substances.
(2) Biological products.
(3) Cultures and stocks.
(4) Exempt human or animal specimens.
(5) Patient specimens.
(6) Regulated medical waste.
(7) Sharps medical waste.
(8) Toxins.
(9) Used health care products.
[Delete the text of 346.311 in its entirety.]
346.32 Division 6.2, Infectious Substances Packaging, Marking, Labeling, and Documentation
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Exhibit 346.32
Packaging References for Mailable Materials, Infectious Substances (Hazard Class 6, Division 6.2)
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[Revise the last sentence of footnote 2. of Exhibit 346.32 to read as follows:]
2. ***A Division 6.1 toxin that can qualify as Limited Quantity surface is permitted when packaged in accordance with 346.31(b) or 346.22.
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346.327 Exempt Human or Animal Specimens
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[Revise the text of item a. to read as follows:]
a. Primary Receptacle Requirements: A single primary receptacle must not contain more than 500 milliliters (ml) of a liquid specimen or 500 grams of a solid specimen. Multiple primary receptacles may be enclosed within a single secondary packaging, provided the combined volume does not exceed 500 ml (for liquids) or 500 grams (for solids). Each primary receptacle must be leakproof or sift proof and individually wrapped or separated with material sufficient to protect it and contain or absorb the total amount of liquid or solid in case of leakage or breakage.
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347 Radioactive Materials (Hazard Class 7)
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347.2 Mailability
[Add the following new section number and title between the section number and title of 347.2 and the current introductory text of 347.2 to become the section number and title of the current introductory text, and renumber current sections 347.21 and 347.22 to new 347.22 and 347.23, respectively:]
347.21 General
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[Revise item a. to read as follows:]
a. International Mail: Radioactive materials bearing or required to bear a Class 7 Radioactive White-I, Radioactive Yellow-II, or Radioactive Yellow-III hazardous materials warning label (refer to Exhibit 325.3) are prohibited. Specific admissibility requirements for international shipments of radioactive material are detailed in 622.3 and IMM 135.5. The radioactive activity content must not exceed one-tenth of the limits outlined in Exhibit 347.23.
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347.23 Mailable Radioactive Materials
[Revise the introductory text of renumbered 347.23 to read as follows:]
As stated in 347.21, the only categories of radioactive material that are mailable in international mail or in domestic mail via surface transportation are those that do not have an activity level exceeding the limits in Exhibit 347.23 and are eligible under 49 CFR to be shipped as excepted packages for:
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[Renumber current Exhibit 347.22 to new Exhibit 347.23.]
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347.5 Emergency Procedures
[Revise the text of 347.5 to read as follows to correct bullet formatting:]
The following apply:
a. In cases where a nonmailable package of radioactive material is found in the mailstream, the following procedures must be immediately followed:
(1) Place the package at least 15 feet from other mail or personnel. Under no circumstances may the package be dispatched.
(2) Report the mailpiece to the appropriate officials in accordance with POM 139.117 and 139.118, as applicable.
(3) If a package of radioactive material is damaged or is leaking, immediately contact the facility safety officer (or designee). The safety officer will:
(a) Follow the appropriate spill-response procedures.
(b) Isolate the area around the damaged package to prevent contact with people.
(c) Isolate any conveyor, belt, chute, or other equipment or conveyance, including mailbags, in which the radioactive material has leaked or may have leaked.
(d) Rope off or guard the isolated area whenever practical.
(e) Place a temporary sign indicating the presence of radioactive materials and bearing a warning to stay beyond the edge of the roped area.
b. The local postmaster or facility manager must immediately request the assistance of qualified persons to check radiation hazards and to supervise the salvage and decontamination. This assistance may be received from the mailer (if known) or from one of the following contacts:
(1) Nearest office of the Department of Energy (DOE) as listed in Exhibit 347.5 or DOE’s national emergency number and website:
DEPARTMENT OF ENERGY (DOE)
EMERGENCY OPERATIONS CENTER
Telephone: 202-586-8100
doe.gov
(2) Local health, fire, or police departments.
(3) Local civil defense authorities.
(4) Nearby military installations.
(5) Nearby scientific laboratories.
(6) The Nuclear Regulatory Commission, the Environmental Protection Agency, and the Federal Emergency Management Agency, whose national emergency numbers and websites are as follows:
NUCLEAR REGULATORY COMMISSION (NRC)
Telephone: 301-816-5100
nrc.gov
ENVIRONMENTAL PROTECTION
AGENCY (EPA)
NATIONAL RESPONSE CENTER
Telephone: 800-424-8802
epa.gov
FEDERAL EMERGENCY MANAGEMENT
AGENCY (FEMA)
NATIONAL EMERGENCY COORDINATION
CENTER
Telephone: 202-646-2400
fema.gov
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6 International Mail
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62 Dangerous Goods: International Mail
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[Revise the title of 621 to read as follows:]
621 General Requirements
[Delete section number 621.1 and its title “Mailing Conditions” and place section 621.1’s text under the section number and title of 621.]
[Revise the text of 621 to read as follows:]
In international commerce, hazardous materials are referred to as “dangerous goods.”Almost all dangerous materials are prohibited in international mail. The only mailable dangerous materials are the following:
a. Certain infectious substances;
b. Excepted quantities of radioactive material that are allowed in domestic mail;
c. Certain magnetized materials; and
d. Certain lithium and lithium-ion batteries.
Exhibit 621 provides a summary of the types of dangerous materials that are eligible for mailing in international mail.
The few types of dangerous materials that are generally permitted in international mail may be further restricted by the mailing limitations imposed by an individual country. Because individual countries have unique prohibitions and restrictions, it is always necessary to consult the ICL in the IMM to be certain that an otherwise mailable dangerous material is acceptable for shipment to a specific country.
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[Renumber current Exhibit 621.1 to new Exhibit 621.]
Exhibit 621
DOT Hazard Classes and Mailability for International Mail
[Revise the text of renumbered Exhibit 621 to read as follows:]
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622 Mailable Dangerous Goods
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622.2 Biological Substances (Division 6.2)
[Revise the text of items d., e., and f. to read as follows, respectively:]
d. Mailability and Packaging Requirements: Mailable infectious substances must be prepared according to 346.321 and Packaging Instruction 6C.
e. Volume and Packaging Limits: Mailable infectious substances are limited to 50 milliliters for liquids or 50 grams for solids per mailpiece. Packaging must comply with 346.321 and Packaging Instruction 6C in Appendix C, and the requirements in IMM 135.31 and 135.41.
f. Nonregulated and Exempt Specimens: Nonregulated materials defined in 346.325 and exempt human or animal specimens defined in 346.12(d) are mailable between eligible institutions (see item c.) when properly packaged in accordance with Packaging Instructions 6G and 6H in Appendix C and comply with 346.325 through 346.327 and IMM 135.42.
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622.3 Radioactive Materials (Class 7)
[Revise the text of item b. to read as follows:]
b. Mailability and Packaging Requirements: Mailable radioactive materials must be packaged in accordance with Packaging Instruction 7A in Appendix C and the requirements specified in IMM 135.5.
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[Revise the text of item f. to read as follows:]
f. Labeling and Marking: The sender is responsible for supplying and affixing the following information to the address side of the package:
(1) Radioactive Materials, Quantities Permitted for Movement by Post.”
(2) “Return to Sender in Case of Nondelivery.”
(3) A white package label with the French text “Matières Radioactives.”
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Appendix C
USPS Packaging Instructions for Mailable Hazardous Materials
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USPS Packaging Instruction 6C
Category B Infectious Substances
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Mailability
n International Mail: Mailable only when:
[Delete the last bullet under “International Mail: Mailable only when:” in its entirety.]
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Outer Packaging
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[Revise the text of the third bullet to read as follows:]
n A poly-type mailer bag covering may be acceptable as the outer packaging provided triple packaging is complete, the selvage edge of the wrapping is less than 2 inches, and the required markings and address information are applied both on the interior rigid box and the additional outer polybag wrapping. Note: A poly-type mailer bag is not permitted for use as an outer package in international mail.
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USPS Packaging Instruction 6F
Forensic Material
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Mailability
n International Mail: Mailable only when:
[Revise the bulleted text of the first bullet “International Mail: Mailable only when:” to read as follows:]
– The conditions in 622.2 are met.
– They are permitted by the destination country. (Refer to the Individual Country Listing in the IMM.)
– They are presented by and to authorized laboratories designated in “International Mail” below in this Packaging Instruction.
– They meet the Category B infectious substance definition in 346.12(a).
– The director, Product Classification, has granted written approval.
– They are triple-packaged (refer to below), meeting the packaging requirements in 49 CFR § 173.199.
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USPS Packaging Instruction 6H
Exempt Human or Animal Specimens
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Mailability
[Revise the text of the first bullet, “International Mail: Mailable,” to read as follows:]
n International Mail: Mailable. They are not subject to regulation as hazardous materials but are required to be sent between eligible institutions and when presented for mailing, they must be prepared following 346.327, 622.2, and as outlined below.
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Required Packaging
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Secondary Packaging
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[Delete in its entirety the second bullet under “Secondary Packaging.”
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[Add a new “Outer Packaging” section after “Secondary Packaging” and before “Marking/Documentation” to read as follows:]
Outer Packaging
n The primary and secondary packaging must be enclosed within rigid outer packaging (see 339.4).
n At least one side of the outer packaging must measure a minimum of 3.9 inches by 3.9 inches (100 millimeters × 100 millimeters).
Marking/Documentation
[Revise the text in the section “Marking/Documentation” to read as follows:]
n Labels and markings must be placed on the address side of the mailpiece unless specified differently in 221.1 and 325.1.
n The outer packaging must be marked on the address side with “Exempt Human Specimen” or “Exempt Animal Specimen,” as appropriate.
n Shipping documentation is not required.
USPS Packaging Instruction 7A
Radioactive Materials
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Mailability
[Revise the text of the first bullet, “International Mail,” to read as follows:]
n International Mail: Only as permitted in 622.3 and IMM 135.5, and when sent under the following conditions:
– Sent only to countries that expressed a willingness to accept them. (Refer to the Individual Country Listings in the IMM.)
– APO/FPO/DPO destinations are subject to the conditions prescribed by the U.S. Department of Defense (DOD) as listed in “Overseas Military/Diplomatic Mail” in the Postal Bulletin.
– Mailable radioactive materials may not have an activity content that exceeds one-tenth of the limits specified in Exhibit 347.22 and must not contain uranium hexafluoride.
– The sender must apply his or her name and address and list the contents of the item on the inner wrapping.
– Mailable radioactive materials may not have an activity content that exceeds one-tenth of the limits specified in Exhibit 347.22.
– Each shipment must comply with both the International Atomic Energy Agency Regulations and the specifications in 347 and this section.
– The sender and recipient of each radioactive materials shipment must receive prior authorization from the appropriate regulatory authorities within their countries.
– The address side of each mailpiece must bear the following endorsements in bold letters: “Return to Sender in Case of Nondelivery” and “Radioactive Materials, Quantities Permitted for Movement by Post” and the applicable UN-number (i.e., UN2909, 2910 or 2911)
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Index
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I
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Infectious substances, 346
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[Revise the reference “Mailable material, 346.311” to read as follows:]
Mailable material, 346.31(b)
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R
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Radioactive materials, 347
[Revise the reference “Articles and instruments, Exhibit 347.22” to read as follows:]
Articles and instruments, Exhibit 347.23
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The Postal Service will incorporate these revisions into the next edition of the online Publication 52, which is available via Postal Explorer® at pe.usps.com.
— Product Classification,
Product Solutions, 4-16-26
