We analyzed genetic effects of ethylmethanesulfonate (EMS) on mature sperm of males of the Drosophila melanogaster MS, w strain. The frequency of induced mutations was estimated in the X chromosome, in five loci of chromosome 2 (b, j, pr, cn, and vg), and in eight loci of chromosome 3 (ru, h, th, st, cu, sr, es, and ca). Mutability was significantly increased in the genetically unstable MS, w strain in comparison with the reference laboratory ss, w strain. In MS, w, genetic instability was characteristic of more than 50% EMS-induced mutations. Analysis of the mutation spectrum revealed a specific distribution along the chromosomes. In MS, w, exhibition of spontaneous and induced instability was shown to be similar. This could imply a common mechanism of control of mutability involving transpositions of mobile genetic elements.