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 merozoite^1–3 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 sera^6,7. 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.