Iraq, for instance, is known to have made anthrax weapons before the 1991 Persian Gulf war and is suspected of having them today.

Mr. Blix is said to have demurred, saying that the burden was on Iraq to prove that it had destroyed any anthrax weapons.

Terrorists have tried and failed to make anthrax weapons.

The hurdles to making anthrax weapons include getting the right strain of the bacteria.

The Florida Case Is the Florida case a military-type anthrax weapon?

Saddam Hussein is producing his anthrax weapon for a clear purpose: to credibly threaten us with its use.

"It's not inconceivable," Dr. Fraser said, "that at some point we could make an association between a molecular fingerprint" and the source of the anthrax weapon.

Different countries that made anthrax weapons had different techniques for achieving the small size needed to penetrate deeply into human lungs.

Dr. Spertzel said the removal of electrostatic charges - making them "slippery" - was as important as particle size in creating an effective anthrax weapon.

"The bad guys have the anthrax weapon and the vaccine that we are using works."