The chromosomal relationships between the Japanese water shrew Chimarrogale platycephalus and the Eurasian water shrew Neomys fodiens were investigated by conventional and differential staining. From the side-by-side analysis of matching G-banding patterns from the two species, a high degree of G-band homology was recognized in most of the chromosomes that were compared, although the extent of such homology was unclear in several small chromosomes. In C. platycephalus, large blocks of C-heterochromatin (C-blocks) were found in pair nos. M1, M8, M10 and ST23 and in the Y chromosome as conspicuous C-bands, while N. fodiens had no such C-blocks, having centromeric C-bands on most chromosomes with the exception of several small pairs, which included ST1 and ST23. Silver-stained nucleolus organizers (Ag-NORs) were found only on the secondary constriction of pair no. 1 in C. platycephalus and on the minute short arms of ST23 and ST24 in N. fodiens. A discussion of interspecific differences in C-banding patterns, as well as in the locations of Ag-NORs, is presented, focusing on the direction of alterations in these cytogenetic features. We propose that Chimarrogale might have differentiated from a fodiens-like ancestor through chromosomal alterations, such as formation of C-blocks, translocation of NORs, and other rearrangements.