The N-terminal amino acid sequences of the 42- and 36-kDa Plasmodium falciparum (strain FCB1) merozoite surface polypeptides, both processing fragments from the 185-195-kDa polymorphic glycoprotein, have been obtained. The N-terminus of the 42-kDa fragment is located in the amino acid sequence of the precursor molecule at amino acid residue 1255 (numbering according to Mackay, M., Goman, M., Bone, N., Hyde, J.E., Scaife, J., Certa, U., Stunnenberg, H. and Bujard, H. (1985) EMBO J. 4, 3823-3829). The peptide bond cleaved during processing is Glu-Ala. This fragment is derived from the C-terminal end of the precursor molecule. The N-terminus of the 36-kDa fragment is located in the precursor molecule at amino acid residue 902 (numbering as above), and the bond cleaved is Asn-Asp.