Sprague-Dawley rats were exposed to the stress of restraint, heat and bright lights three times daily from Days 14 to 22 of gestation. Because prepartal stress did not markedly disturb the mother's retrieving and crouching behavior, disturbances in postpartal nursing behavior do not seem to account for the abnormal sexual behavior of male offspring as adults. The most significant finding was that litter weights were reduced, not only at birth, but for 3 weeks thereafter, suggesting that prepartal stress not only altered the pups in utero but also affected postpartal milk synthesis. The possibility emerges that prepartal stress may alter adult sexual behavior in males by modifications in fetal and/or maternal pituitary glands.