The purpose of these experiments was to elucidate further the possibility that intraventricular injections of bombesin (BBS) lower the set point around which an animal regulates its core body temperature. In an attempt to prevent a confounding of general activity and thermoregulatory behavior which occurred in earlier work, a horizontal temperature gradient was used. Intraventricular injections of bombesin resulted in the selection of temperatures that were approximately 9-13 degrees C colder than those selected by animals following control injections. Additionally, the increase in core body temperature observed following control injections was reversed by the highest dose of bombesin. No significant alterations in general locomotor activity were observed. These findings suggest that bombesin may act centrally to reduce the set point around which behavioral responses are regulated.