Long-Evans rats, 4-6 weeks of age, were given access to 0, 1, 10, or 100 ppm sodium chlorite in deionized water ad libitum as drinking water. Males were exposed 56 days, and females for 14 days prior to breeding and throughout the 10-day breeding period. Males were evaluated for sperm parameters and reproductive tract histopathology following the breeding period. Females were exposed throughout gestation and lactation. Dams and pups were necropsied at weaning. Decreases in serum T3 and T4 were observed on Postnatal Days 21 and 40 in male and female pups exposed to 100 ppm chlorite or above. Additionally, groups of males were exposed to 0, 10, 100, or 500 ppm ad libitum in the drinking water to confirm observed subtle reproductive effects and examine dose-effect relationships. A significant increase in the percentage of abnormal sperm morphology (P less than 0.001) and decrease in sperm direct progressive movement (P less than 0.01) were observed for adult males at chlorite levels of 100 or 500 ppm. Since other clinical and reproductive endpoints were not affected, sperm morphology and sperm direct progressive movement may be two of the more sensitive indicators of reproductive damage.