Two chromium(VI) compounds (potassium chromate and potassium dichromate) and one chromium(III) compound, chromium chloride, were evaluated for genotoxic effects in the wing spot test of Drosophila melanogaster following standard procedures. This assay detects both somatic recombination and mutational events. The genotoxic effects were determined from the appearance of wing spots in flies transheterozygous for the third chromosome recessive markers multiple wing hairs (mwh) and flare-3 (flr(3)), as well as in flies heterozygous formwh and the multiply inverted TM3 balancer chromosome. Genetic changes induced in somatic cells of the wing's imaginal discs lead to the formation of mutant clones on the wingblade. Single spots are due to different genotoxic mechanisms: point mutation, deletion, chromosome breakage, and mitotic recombination; while twin spots are produced only by mitotic recombination. From our results it appears that both chromium(VI) compounds clearly increase the incidence of mutant clones by inducing high increases in the frequency of all types of clones recorded. On the contrary, chromium(III) did not increase the frequency of mutant clones. A high proportion of the total spot induction was due to mitotic recombination, confirming previously reported data on the strong recombinogenic activity of chromium(VI) compounds.