Local tissue mast cells were found to rapidly secrete their heparin-containing granules in a dose-related response to subcutaneous injection of relatively small amounts of bee venom. The shed granules formed complexes with cationic protein in vivo and these complexes were subsequently ingested by adjacent mononuclear cells. Addition of heparin to bee venom in vitro resulted in the formation of complexes with reduction in both cytolytic and lethal activities of the venom. It is suggested that mast cell granules may, during transfer from mast cells to phagocytic cells, sequester noxious cationic proteins of bee venom and that dermal mast cells may thus be strategically situated and uniquely adapted to serve as a local means of resistance to bee sting.