Intraperitoneal administration of ketamine produced dose-dependent hypothermia at the ambient temperature (T(a)) of both 8 and 23°C in unanesthetized rats. At a T(a) of 8° C, the hypothermia was brought about solely by a decrease in metabolic heat production. There were no changes in either the tail skin temperature (T(tail)) or the sole skin temperature (T(sole)). At a T(a) of 23° C, the hypothermia was due to an increase in T(tail), an increase in T(sole), and a decrease in metabolic heat production. However, at a T(a) of 31° C, there were no changes in rectal temperature in response to ketamine application, since neither heat production nor skin temperatures (e.g., T(tail) and (T(Sole)) was affected by ketamine at this T(a). The data indicate that the effect of the drug treatment may be to decrease heat production and (or) increase heat loss.