In a series of genetic studies of Korean population, genetic polymorphism of mannose phosphate isomerase was investigated in 309 placental samples by using the method of horizontal starch gel electrophoresis. The number of MPI 1-1 and MPI 3-1 phenotypes observed was 299 and 10, respectively. The allele frequencies for Mpi1 and Mpi3 were found to be 0.9838 and 0.0162, respectively, which were similar to those of Chinese and Papua New Guinean in Port Moresby.