The complete nucleotide sequence of the gene for the 230-kDa precursor to the major merozoite surface antigens (PMMSA) of Plasmodium yoelii YM has been determined. A single open reading frame of 5316 bp encodes a protein of calculated molecular mass 197,000. The deduced amino acid sequence contains potential signal peptide and membrane anchor sequences of 19 and 18 residues, respectively, and a region of six tandemly repeated tetrapeptides, Gly-Ala-Val-Pro. Comparison with the 195-kDa Plasmodium falciparum analogue (Pf195) at the amino acid level indicated an overall homology of approximately 30%, with areas of as high as 60% conservation. The tripeptide repeats present near the N-terminus of the Pf195 antigen are absent from the Py230 sequence. The PMMSA can be divided into 22 blocks based upon interspecies amino acid conservation.