We previously demonstrated that rat offspring exposed perinatally to methoxychlor (MXC) still exhibited immunotoxic changes in young adulthood at 10 weeks of age. That result led us to further investigate whether the influence of perinatal exposure to MXC on the rat immune system persistently remains in adult life. Sprague-Dawley rat offspring of both sexes from dams receiving MXC at dietary dose levels of 0, 30, 100, 300, and 1000 ppm were used for the present study. The pups exposed to MXC through the placenta, milk, and/or direct intake during the gestation and lactation periods were maintained on a normal diet from weaning up to 52 weeks of age. At the termination, a significant increase in plasma chloride was noted in both sexes at 300 and 1000 ppm MXC exposure. Females at 1000 ppm MXC exposure showed increases in serum IgM and urinary protein and had significantly increased relative weights (ratio to body weight) of the spleen and kidneys. An increased relative kidney weight was also noted in females at 300 ppm MXC exposure. Histopathologically, the incidence and severity of chronic nephropathy tended to be higher in females at 1000 ppm MXC exposure, and their kidneys had enlarged glomeruli with increased IgG and IgM deposits. In the immune system, however, there were neither notable histological changes nor significant alterations in the splenic lymphocyte subsets for any dose group of either sex. These results indicate that the immunotoxic damage caused by pre- and post-natal MXC exposure appears to be repaired during the process of growth, although the effect seems to remain in females even at 52 weeks after birth and consequently may accelerate the progression of chronic nephropathy.