DNA-specific sequences from an enzyme-coding gene (glutamate dehydrogenase, gdh), a regulatory protein-coding gene (E74) and genes of the actin family were mapped by in situ hybridization on the polytene chromosomes of six species representative of the geographical distribution of the Drosophila montium subgroup of the melanogaster species group. In all species studied, one hybridization signal was detected for the gdh and E74 genes, and seven signals for the actin genes. The distribution of the actin-related loci in five montium species is similar to that of the other Drosophila species studied so far, although they present an extra signal. This distribution differs in the sixth montium species studied, D. kikkawai. Taking into account the present results, as well as previous data obtained mainly by in situ hybridizations, homologies among the polytene chromosomes of the montium subgroup species, as well as between these species and D. melanogaster, were also established.