We investigated the effect of alveolysin on human granulocytes. Alveolysin is an exoprotein produced by Bacillus alvei and belongs to the group of sulfhydryl-activated cytolysins. Other members of this group are streptolysin O and theta-toxin from Clostridium perfringens. It is demonstrated that alveolysin leads to leukotriene generation from human granulocytes, which exert chemotactic (leukotriene B4) and slow-reacting substance (leukotriene C4, D4, and E4) activity under sublytic concentrations.