Infected with fear: talk of biological and chemical terrorist attacks has some Americans fearing the worst is yet to come. How safe are you?

• Author: McCollum, Sean

THE DISPLAY STAND WAS BARE, AND ITS BASE WAS littered with empty boxes. "No, we're out of gas masks," the clerk in a New York City army-navy surplus store told three customers in quick succession. She pulled out a clipboard. "But we've got a waiting list."

The store's security guard, watching the scene, shook his head. "People are just irrational right now," he said.

Since the September 11 terrorist attacks and the mysterious spread of anthrax through the postal system, fears of biological and chemical attack have taken hold of many Americans. The most nervous hound doctors or search the Internet for supplies of Cipro, a powerful anthrax-killing antibiotic. A new book on bioterrorism, Germs, is on the best-seller lists. And the arrival of the day's mail has become a source of worry.

The number of anthrax deaths had reached only four by early November, but several more people were infected with the highly lethal inhaled form of the disease. Early government efforts to find the source were unsuccessful, and public health officials had to rethink their understanding of anthrax and how it spreads. Faced with even a limited attack, officials finally acknowledged that the threat was more serious than they had believed.

The effects of the scare have rippled far beyond those killed, causing temporary closures of the House of Representatives, the Supreme Court building, and several postal facilities, disrupting mail deliveries. As a precaution, thousands of people have been taking antibiotics to ward off possible infection.

Yet despite the widespread fears, experts on chemical and biological weapons maintain that it is extremely difficult for terrorists to pull off attacks on a grand scale.

"The public and far too many policy makers do not understand the substantial technical hurdles associated with making and dispersing chemical and biological weapons so that massive casualties result," says Amy Smithson, an expert on biological and chemical weapons at the Henry L. Stimson Center, a private group in Washington, D.C. "That's why people usually believe the worst of what they hear."

U.S. intelligence agencies believe terrorist groups, including Osama bin Laden's Al Qaeda network, have experimented with chemical weapons. Such weapons include:

* Blister agents--gases or liquids that burn and blister tissue. One example is mustard gas, widely used in World War I.

* Blood agents--cyanide and other poisons in vapor form that prevent the body from using oxygen, causing suffocation.

* Nerve agents--distributed in gas or liquid...