Protective immune responses against the asexual stages of the human malaria parasite, Plasmodium falciparum, are most probably directed against exposed antigenic determinants on the surface of the free merozoite1-3 or the infected red blood cell4, and therefore antigens in these locations are candidates for testing as components of a defined molecular vaccine. To facilitate the search for such antigens, we recently developed a method for the expression of P. falciparum proteins in Escherichia coli as fused polypeptides5. Many clones producing antigens were detected by screening with immune human sera6,7. We show here that antibodies against the fused polypeptide expressed by one such clone react with a P. falciparum protein that is synthesized late in schizogony and is later present on the surface of the ring-infected erythrocyte. The protein is composed of repeating subunits of 8, 4 and 3 amino acids and is present in all isolates of P. falciparum examined.