Anthrax toxin can induce hemolysis in the presence of polymorphonuclear cells (PMNs), an activity primarily mediated by protective antigen, with synergic effects provided by lethal factor and edema factor. Lethal factor and edema factor, individually or in combination, are incapable of lysing red blood cells. The requirement for the presence of PMNs indicates that hemolysis associated with Bacillus anthracis infection is indirect rather than direct, as observed in many other bacterial infections.