1. The oxygen consumption (VO2) of unrestrained rats given a 'cafeteria' (high energy, high fat) or control diet was studied. The resting values of VO2 were the same in each dietary group, whether maintained at 26 degrees C or 6 degrees C. This negative finding suggests that cafeteria feeding is not an important cause of diet-induced thermogenesis (DIT). 2. The response of each group of rats to injected noradrenaline or dopamine was also studied. Each catecholamine could increase VO2 values but the response was much less in cold-adapted rats measured at 6 degrees C. In all experimental circumstances the dopamine response exceeded that of noradrenaline. There was no evidence that the cafeteria diet consistently increased the response to either catecholamine. 3. These results suggest that DIT cannot be equated with non-shivering thermogenesis (NST). Furthermore, it is suggested that dopamine would be a better agent for measuring the oxygen equivalent of NST, since it would stimulate the dopamine receptors as well as the alpha- and beta-adrenoreceptors of brown fat.