Abstract: The abilities of McAbs to enhance the phagocytosis of Plasmodium falciparum by peritoneal macrophages and the killing of parasites by peritoneal cells free of adherant cells were evaluated by in vitro assay. Four of six McAbs, which recognized parasite antigens expressed only on segmentors and free merozoites of P. falciparum by immuno-fluorescence, augmented the phagocytosis of the parasites 2-4 times that of SP2/0 ascitic fluid. Enhanced McAbs-media ted phagocytosis as a result of opsonization of the parasite was demonstrated by preincubating macrophages with McAbs prior to the phagocytic assay. Four of seven McAbs examined showed cytotoxic activity on P. Jalciparum. Peritoneal cells free of adherent cells were capable of killing the parasites in the presence of McAb. The results indicate that there may be "mono-function", "bifunction" and "multi-function" types of McAbs against P. Jalciparum. The putative protective antigen of malaria parasite purified by "multifunctional McAb" affinity chromatotraphy may have potential interest as a vaccine against the parasite or as an immunodiagnostic material.