The body temperature in male rats born to mothers treated with saline or imipramine (5 mg/kg, IMI-F1) from day 1 to day 21 of gestation showed a significant decline between 8 and 13 weeks of age. The magnitude of the decline was greater in the IMI-F1 rats than in saline-F1 rats. In contrast, the body temperature in the IMI-F1 female rats showed a significant rise between 8 and 13 weeks of age. Adult IMI-F1 male rats showed a significant hyperthermia for 1-2 h after an injection of chlorpromazine while the littermate female rats and the control male and female rats showed a marked hypothermia. The results suggest that prenatal exposure to imipramine induces sex-related alterations in the thermoregulatory centers.