A partitional calorimetry study compared thermoregulatory responses of unanesthetized adult rhesus monkeys (4 female, 1 male) to those anesthetized with ketamine HCl and exposed to ambient temperature (Ta) of 18, 29, 38 degrees C. Steady-state metabolic heat production (M), mean skin temperature (Tsk), rectal temperature (Tre), respiratory evaporative heat loss (Eres), and total evaporative heat loss (Etot) were measured at each Ta. Average Tre of anesthetized animals was reduced by approximately 1 degree C at Ta 18 degrees C, but thermal balance in anesthetized and control animals was maintained by reflexly decreased tissue conductance and shivering. For anesthetized animals, the average M increased 1.8 times over the lowest value of 40.13 W/m2 at Ta 29 degrees C, compared to a 1.5-fold increase for controls. Responses for both groups were not different at Ta 29 degrees C, both groups regulated body temperatures by vasodilation and increased sweating, but with ketamine sweating was reduced (35%). Effective tissue thermal conductance (K) was lowest at Ta 18 (10.8 W/m2 . degrees C) and increased to 39.4 W/m2 . degrees C at Ta 38 degrees C. No significant difference in K was found between ketamine and control groups at other Ta's.