The Centers for Disease Control and Prevention sent samples directly to several Iraqi sites that United Nations weapons inspectors determined were part of Saddam Hussein's biological weapons program, CDC and congressional records from the early 1990s show.
Iraq had ordered the samples, claiming it needed them for legitimate medical research.
The CDC and a biological sample company, American Type Culture Collection, sent strains of all the germs Iraq used to make weapons, including anthrax, the bacteria that make botulinum toxin and the germs that cause gas gangrene, the records show. Iraq also got samples of other deadly pathogens, including West Nile virus.
The transfers came in the 1980s, when the United States supported Iraq in its war with Iran. They were detailed in a 1994 Senate Banking Committee report and a 1995 follow-up letter from the CDC to the Senate.
The exports were legal at the time and approved under a program administered by the Commerce Department.
"I don't think it would be accurate to say the United States government deliberately provided seed stocks to the Iraqis' biological weapons programs," said Jonathan Tucker, a former U.N. biological weapons inspector. "But they did deliver samples that Iraq said had a legitimate public health purpose, which I think was naive to believe, even at the time."
The disclosures put the United States in the uncomfortable position of possibly having provided the key ingredients of the weapons America is considering waging war to destroy, said Sen. Robert C. Byrd.
The West Virginia Democrat entered the documents into the Congressional Record this month.
Byrd asked Defense Secretary Donald H. Rumsfeld about the germ transfers at a recent Senate Armed Services Committee hearing. Byrd noted that Rumsfeld met Hussein in 1983, when Rumsfeld was President Reagan's Middle East envoy.
"Are we, in fact, now facing the possibility of reaping what we have sown?" Byrd asked Rumsfeld after reading parts of a Newsweek article on the transfers.
"I have never heard anything like what you've read, I have no knowledge of it whatsoever, and I doubt it," Rumsfeld said.
He later said he would ask the Defense Department and other government agencies to search their records for evidence of the transfers.
Invoices included in the documents read like shopping lists for biological weapons programs.
One 1986 shipment from the Virginia-based American Type Culture Collection included three strains of anthrax, six strains of the bacteria that make botulinum toxin and three strains of the bacteria that cause gas gangrene.
Iraq later admitted to the United Nations that it had made weapons out of all three.
The company sent the bacteria to the University of Baghdad, which U.N. inspectors concluded had been used as a front to acquire samples for Iraq's biological weapons program.
The CDC, meanwhile, sent shipments of germs to the Iraqi Atomic Energy Commission and other agencies involved in Iraq's weapons of mass destruction programs.
It sent samples in 1986 of botulinum toxin and botulinum toxoid - used to make vaccines against botulinum toxin - directly to the Iraqi chemical and biological weapons complex at al-Muthanna, the records show.
Botulinum toxin is the paralyzing poison that causes botulism. Having a vaccine to the toxin would be useful for anyone working with it, such as biological weapons researchers or soldiers who might be exposed to the deadly poison, Tucker said.
The CDC also sent samples of a strain of West Nile virus to an Iraqi microbiologist at a university in the southern city of Basra in 1985, the records show.