The Pentagon says it mistakenly sent out anthrax spores to as many as nine laboratories.
The labs were supposed to receive dead anthrax samples for research use.
Pentagon spokesman Col Steve Warren said it was working with the Centers for Disease Control and Prevention (CDC) to retrieve the samples.
The government has confirmed one shipment contained live spores and it is believed the other eight also did.
Col Warren says there are thought to be no risks to the public.
The US Defence Department said it had launched an investigation into how the blunder occurred.
The live spores came from Dugway Proving Ground in Utah, a military facility that was trying to develop a test to identify biological threats, said the Pentagon.
The samples were shipped to government and commercial labs in Texas, Maryland, Wisconsin, Delaware, New Jersey, Tennessee, New York, California and Virginia.
Contact with anthrax spores can be deadly.
Only last year, it emerged that dozens of laboratory workers at the CDC in Atlanta, Georgia, were possibly exposed to live anthrax.
Staff were not wearing full protective gear as they came into contact with the samples because they thought the spores were safe.
No one was reported to have been made ill.