Thermoregulatory variables were measured in captive beluga and killer whales to confirm earlier work on smaller cetaceans. Whales had body temperatures within mammalian range and maintained a skin-water temperature difference of about 2° C. Heat-loss coefficients were less than that reported for humans. Thermal conductance may be greater than or equal to small cetaceans and humans. The larger killer whales had smaller surface-area-to-volume ratios than the belugas, as expected. However, the largest whales of each species had a greater surface area devoted to the appendages. Respiratory evaporative energy losses were small owing to expired air that was cooler than core temperature and that was unsaturated with water vapor. Basal or resting metabolic rate was higher than expected for animals of their body weight. The best-fit regression equation for our data was metabolic rate =$0.88 mass^{1.06}$. It is not clear whether increased metabolic rates were necessary to compensate for heat loss or, conversely, higher heat-loss coefficients are necessary to dump heat generated by high metabolic rates and a small surface-area-to-volume ratio.