The ability of cyclohexanone to induce sex-linked recessive lethal mutations in the post-meiotic germ cells was evaluated in Drosophila males (wild-type stock, Canton-S). Based on preliminary toxicity determinations, Drosophila (689, 1343, 1008 and 892/treated groups and 559, 1203, 1213, and 892/control groups) were treated with cyclohexanone via inhalation at vapor concentrations of 0 (control group) or 36% for 4 hours. Surviving flies were mated with 3 sets of 3 virgin 'Basc' females for 72 hours each. Percent mortalities during exposure and the following 21 hours averaged 32% in the treated groups versus 0% in the controls. Male sterility was slightly increased in treated flies. There was no indication of any mutagenic effect in any germ cell stage in treated male Drosophila (percent lethals for treated and control groups were 0.071% and 0.070%, respectively).