Blood samples ofMacaca irus imported from Cambodia and the Philippines were examined by starch gel electrophoresis for red cell acid phosphatase, phosphoglucomutase, and hemoglobin variations. Two different types, each showing two and three zones with acid phosphatase activity, were observed in 172 cynomolgus monkeys. Variant (less common) type was detected in only eight of 113 in the Cambodian group. Individual differences in the distribution of phosphoglucomutase isoenzymes were also found in the monkey samples. Five different types were distinguished in 145 samples examined, but no possible explanation for genetic control can be given for the observed patterns. In addition to the usual hemoglobin found in all the hemolysates, fastmigrating hemoglobin components were demonstrated in 36% of 172 samples. A striking difference in the distribution of the hemoglobin types was found between the Cambodian and the Philippine groups. The obtained results probably indicate the existence of strong geographical effects on protein polymorphisms in cynomolgus monkey.