Anthrax immune globulin is being developed as a possible response to a bioterror attack. Mortality from the anthrax letters attack in 2001 was 45 percent.

Preliminary animal studies by the Centers for Disease control show that AIG can protect against anthrax before exposure. But they also found that AIG does not protect if it is given after infection -- and can be deadly itself if it is improperly formulated.

Dr. Meryl Nass, an anthrax expert and a physician in Bar Harbor, Maine, said she would become concerned if officials tried to use it on an emergency basis in the event of another anthrax attack.

"Obviously they can't use this stuff," she told UPI. "It might kill people."