These studies were designed to determine the dose-response autonomic and behavioral thermoregulatory effects and the motor effects of dopamine (DA) and prostaglandin E1 (PGE1) injected into the lateral cerebral ventricles of rats. These studies were made possible with a computer-controlled thermocline that permits freely moving rats to select preferred ambient temperatures ranging between 7 and 39 degrees C. All rats were studied with the thermocline gradient both on and off to control for nonspecific effects. PGE1 (0, 0.1, 0.2, 0.5, 1.0 micrograms) produced a dose-related increase in core temperature and produced a dose-related selection of warmer ambient temperatures. Dopamine (0, 50, 100, 200, 400 micrograms) produced a dose-related hypothermia and cold-seeking behavior. Without the gradient, DA-injected rats did not become as hypothermic as in the gradient-on condition. When the gradient was available, rats showed a significant rebound increase in core temperature 50-80 min after DA which did not occur when the gradient was off. Overall, DA induced increases in motor activity, but, during the first 10 min after injection while the gradient was on, the rats made stable selections of cool ambient temperatures and showed reduced activity. Conversely, the behavioral effect of PGE1 did not facilitate the autonomically mediated heat gain. These results emphasize the necessity of creating behavioral options for animals in order to fully evaluate drug effects on thermoregulation.