Experiments on the primary structure of a histidine-rich polypeptide isolated from the malarial parasite Plasmodium lophurae indicate that the smaller quantities of amino acids other than histidine form an integral part of the polypeptide and do not arise from a protein contaminating a histidine homopolymer. In culture, the parasites incorporate over 50% of exogenously supplied histidine into the histidine-rich polypeptide and this incorporation is inhibited by puromycin.