To extend the data on the possible genotoxic effects of organophosphorus pesticides, the insecticide fenitrothion was tested for the induction of gene and chromosome mutations in male germ cells of Drosophila melanogaster. Sex-linked recessive lethals, total and partial sex-chromosome losses and non-disjunction were studied following different exposure methods: adult feeding, injection and larval feeding. In the tests assaying for recessive lethals, we used a MRA strain resistant to malathion. Our results indicate that fenitrothion, at concentrations ranging from 50 to 150 p.p.m., is unable to induce any kind of genetic damage in D. melanogaster, at least under the conditions of testing. © 1987 IRL Press Ltd.