This study examined the effects of cocaine HCl and ambient temperature on the core body temperature of the rat. To further examine the mechanisms of cocaine-induced changes in temperature regulation, the effects of cocaine on behavioral thermoregulatory responses were also observed. At normal room temperature (20 degrees C) cocaine produced a reduction in core body temperature. At a higher ambient temperature (27 degrees C), however, cocaine produced hyperthermia. When given a choice between normal and warm environments, cocaine-injected animals spent significantly less time in the warm environment than did control animals, but had significantly lower core body temperature. These results suggest that cocaine treatment may lower the thermoregulatory set point.