The organophosphorus insecticide dimethoate was tested for induction of genetic damage in male germ cells of Drosophila melanogaster. Sex-linked recessive lethals, sex-chromosome loss and non-disjunction induction were studied following different routes of administration: adult feeding, injection and larval feeding. Our results show that, after injection, dimethoate induces a slight but significant increase in the frequency of point mutations.