The complete nucleotide sequence of the coding region of the circumsporozoite antigen gene (CS gene) of the Nuri strain of the malarial parasite Plasmodium knowlesi is presented. The gene from the Nuri strain exhibits a novel form of sequence diversity when compared to the CS gene from the H strain. Instead of the 12 tandem repeating 36-base pair units of the H strain, the Nuri strain contains 16 tandem repeating 27-base pair units of a different nucleotide sequence that encodes a different repeating peptide. In contrast, the 5' and 3' coding and noncoding sequences flanking the repeats are 98 percent conserved in both strains.