Abstract: Novel antigenic polypeptides having at least one determinant immunologically cross-reactive with determinants on a polypeptide associated with the rhoptry organelles of the merozoite form of the malaria parasite Plasmodium falciparum are described. Also described are immunogenic compositions containing such a polypeptide, DNAs coding for such a polypeptide, recombinant vectors containing such a DNA sequence, host organisms containing a replicable vector, and antibodies which are directed against a polypeptide in accordance with the invention. In addition, processes for the production of the immunogenic compositions, the microorganisms, and the antibodies, as well as the use the polypeptides and the immunogenic compositions for the immunization of mammals against malaria are also described.