We have investigated how differences in environmental temperature interact with diet-content and palatability to affect body weight and energy intake. Adult male hooded Lister rats kept at 18 degrees C or 25 degrees C became obese after over-consumption of palatable, high energy foods. The difference in body weight between the obese rats kept at 18 degrees C and their chow-fed control group was in part attributable to reductions in the growth of the controls kept at 18 degrees C. The obese rats at 18 degrees C had greater body weight gains relative to chow-fed controls than equivalent groups at 25 degrees C. All groups at 18 degrees C had greater energy intakes than equivalent groups at 25 degrees C. Withdrawal of high energy foods led to greater weight loss in rats which had been eating a diet which was varied every day than in rats which had been eating three constantly available high energy foods. Weight losses after diet withdrawal were also greater in obese groups kept at 18 degrees C than in those kept at 25 degrees C. Carcass fat determinations demonstrated that the varied diet-withdrawn rats kept at 18 degrees C did not have persistently elevated body fat stores, but the other diet-withdrawn groups were persistently obese. Therefore lower environmental temperature, and enhanced diet-palatability interact additively to increase energy intakes during cafeteria feeding, and to increase weight losses after withdrawal of palatable foods.