Rana japonica has been reported to be of the male heterogametic type in the sex-determining mechanism. In order to detect the sex-linked loci in R. japonica, the linkage relationships between the sex-determining genes and 11 loci controlling eight enzymes and one blood protein were examined in 48 crosses involving 30 males heterozygous at these loci from 10 local populations by using starch-gel electrophoresis. The Ab locus was found to be linked with the sex-determining genes in the Munakata, Yamaguchi, Ochi, Saiki, Saijo, Sahara and Mobara populations, whereas the MDH-B, MPI, Pep-A and Pep-C loci were not linked with the latter in 23 crosses involving 16 heterozygous males from the seven populations. The MPI locus was linked with the sex-determining genes in the Ichinoseki and Toyama populations, whereas the Ab locus was not linked with the latter in 11 crosses involving eight heterozygous males from two populations. In the Akita population, none of the Ab, AAT-B, ADA, α-GDH, LDH-B, ME-A, ME-B and MPI loci was linked with the sex-determining genes in 14 crosses involving six heterozygous males. Thus, it is evident that the locus linked with the sex-determining gene differs with the populations.