A study was conducted with nitrate to assess the testicular and spermatotoxic effects in mice at doses to which human beings are exposed as well as at higher dose levels in the drinking water. Potassium nitrate was administered to mice at dose levels 90, 200, 500, 700 and 900 ppm for 35 days. There was no difference in the uptake of water in control and treated animals. The amount of nitrate intake/ mouse/day calculated on the basis of water intake in the different groups ranged from 22.5 to 27, 50 to 60, 125 to 150, 175 to 210 and 225 to 270 mg/kg body weight. No changes were evident in the body weight, testicular, epididymal and accessory organ weight at all the dose levels tested, although a decline in sperm count and sperm motility along with an increase in abnormal sperm was noticed at 900 ppm. The activity of marker testicular enzymes, mainly 17-beta hydroxysteroid dehydrogenase (17-betaHSD) and gamma glutamyl transpeptidase (gamma-GT), associated with specific cell types were altered. Histopathological changes including atrophy and disturbed spermatogenesis were observed only at the 900-ppm dose level. In conclusion, we can say that the testicular and spermatotoxic effects are observed only at the highest dose level, which is not likely to be encountered in the drinking water.