Yes, it is, according to US Postal Service regulations, which specify how such samples are to be labeled and packaged.

People having been legally mailing stool samples for years, said David Bull, a spokesman for Beckman Coulter, which makes the widely-used Hemoccult for fecal occult blood testing, which is used as a screening test for possible early colon cancer and for anemia. Though Hemoccult is the industry leader, more than a dozen other companies make stool sample kits that patients send through the mail for testing.

Other potentially hazardous biological materials regularly wend their way across the country via Fedex and other commercial carriers. Diagnostic specimens sent this way, usually by laboratories and hospitals, not individual patients, must comply with standards set by IATA, the International Air Transport Association, said Lourdes Pena, a spokesperson for Fedex.