Five mg/kg of imipramine (IMI) or desipramine (DMI) was injected s.c. to Wistar-Imamichi male and female rats daily from 7 approximately 19 days of age. Control pups received saline. The body temperature of IMI-females showed a significant rise at 7, 8 and 12 weeks of age. Thermic responses to thyrotropin-releasing hormone (TRH, 10 mg/kg, i.p.) at 5 weeks of prepubertal age showed no marked changes. At 9 weeks of age, IMI-males showed a significant hyperthermia 15 approximately 30 min after TRH. Control and IMI-males were castrated at 9 weeks of age. At 11 weeks of age, castrated IMI-males showed a significant decrease in the TRH-induced hyperthermia compared to sham-operated or intact IMI-males. These castrated male rats were treated with a single dose of 20 mg/kg of testosterone enanthate (s.c.) at 11 weeks of age. There was no significant difference in the TRH-induced hyperthermia between the groups when tested at 13 weeks of age. Results suggest that the exposure of the infantile rats to imipramine induces sex-related functional alterations in the thermoregulatory system after puberty and that sex hormones may play a modulatory role for these changes.