Specific sequences derived from the gene for the precursor to the major merozoite surface antigens (PMMSA) of Plasmodium falciparum have been expressed in Escherichia coli and the products have been used to produce antibodies. These antibodies, together with monoclonal antibodies, have been used to investigate the form of the PMMSA protein associated with merozoites. Polypeptide fragments derived by processing from the PMMSA protein have been detected in extracts of merozoites and assigned to locations within the PMMSA coding sequence.