Anthrax is an often fatal disease that is caused by a bacterium. It has been considered a prime biological weapon in the arsenal of terrorists since attacks in the United States in October 2001 and reports elsewhere of anthrax spores being sent through the mail. Harvard Medical School researchers have identified a gene in mice that, in certain forms, renders mice resistant to anthrax. The new findings, which appeared in the October 2001 Current Biology, could aid the effort to defend humans against anthrax in two ways. First, the discoveries could shed light on what happens during the early stages of anthrax infection, and in particular how the lethal toxin released by the bug affects immune cells. This knowledge could be used to devise therapies for human anthrax, which is virtually untreatable once symptoms develop. The findings could help counter the threat of biological terrorism in a second way. “The gene exists and is known to vary in humans,” said William Dietrich, Harvard Medical School assistant professor of genetics and senior author of the study. If these human variants are found to confer immunity, they could provide a basis for screening people who have been exposed to the anthrax bacterium.