Effects of both sodium nitrate (doses of 600 and 1200 mg/kg/day for 3 days) and sodium nitrite (doses of 60 and 120 mg/kg/day for 3 days) on spermatids of mice were investigated by measuring unscheduled DNA synthesis (UDS) 17 days after the end of treatment, and sperm-head abnormality 11 and 17 days after the end of treatment. Neither chemical induced the UDS response in early to mid spermatids (17 days). The only positive result in the sperm-head abnormality test was obtained for the dose of 120 mg/kg/day of sodium nitrite both at 11 and 17 days after treatment. The results presented are in accordance with those of our earlier experiments with the same chemicals, suggesting their nonmutagenic action on the tested germ-cell stages of male mice.