Abstract: Plasmodium falciparum FCCl/HN-infected human erythrocytes were embedded with LR White resin at low temperature. The 185 kDa and 82/41 kDa proteins in erythrocytic stages of P. falciparum were then immuno-labeled by using the protective monoclonal antibodies (McAb)F6-D3 and F6-C2 with protein A-colloidal gold probe. The electron-microscopical observation showed that the 185kDa protein recognized by McAb F6-D3 was located on the surface of free and intracellular merozoites as well as the cytoplasm, plasma membrane, and parasitophorous vaccuole membrane of immature schizonts. The 82/41 kDa proteins identified by McAb F6-C2 was located within the rhoptries of immature schizonts and mature merozoites. These results demonstrated ultrastructurally that the 185 kDa and 82/41 kDa protective antigens were merozoite surface antigen and merozoite rhoptry antigens of P. falciparum FCC1/HN, respectively.