Abstract: Surface antigens of Plasmodium falciparum (schizonts and merozoits) were labeled by the lactoperoxidase-catalyzed iodination method. 125I-labeled P. falciparum (schizonts and merozoites) were dissolved by 1% Triton X-100 and then immunoprecipitated by 11 human immune sera from areas endemic to malaria and 2 normal human sera from areas nonendemic to malaria. Immunoprecipitated target antigens of P. falciparum were analysed by SDS-PAGE and autoradiography.The results showed that there were more than 20 labeled parasite antigens in the Triton X-100 extracts, most of which were recognized by human immune sera. The polypeptides with molecular weights of 270, 240, 200, 183, 160, 137, 104, 98, 74 and 63 KD are major target antigens immunoprecipitated by human immune sera. The polypeptides with molecular weights of 137, 104, 98 and 63 KD of these target antigens could be recognized by human immune sera with more than 3 infections, but could not be recognized by human immune sera with primary infection and normal human sera. It was suggested that these polypeptides might be associated with induced acquired immunity.It was shown that there were common antigen determinants on the surface of P. falciparum and Plasmodium knowlesi (schizonts and merozoites) by crossed immuno-electrophoresis with human immune sera and rabbit anti-P. knowlesi serum.