To characterize the direct effects of wasp and bee venom peptides on mouse peritoneal macrophages, the effects of mastoparan and melittin on phagocytosis were examined. Mastoparan induced an enhancement of phagocytosis in a dose-dependnt manner up to 2x10^<-6>M. Melittin enhanced phagocytosis at lower concentrations, but the dose-response curve was bell-shaped. Even in Ca^<2+>-and Mg^<2+>-free solutions containing EGTA, which reduced extracellular Ca^<2+>, and BAPTA, which reduced intracellular free Ca^<2+>, phagocytosis was enhanced by mastoparan. The results of the present study suggest that the venom peptides, mastoparan and melittin, activate macrophage function.