Rats given restricted feeding and allowed free access to activity wheels increase activity, decrease food intake, and lose body weight compared to nonexercised controls. The phenomenon is of interest because of the relationship between exercise and anorexia nervosa. This study determined if another factor that energizes behavior in rats, water deprivation, produces similar exercise-induced weight loss. Rats were maintained on a restricted water schedule (10 min/day) combined with free access to running wheels and food; controls had no wheel access or were food deprived only. Both water-deprived groups consumed similar amounts of food and water, with the exercised group losing more body weight. Plasma osmolality, hematocrit, and posterior pituitary vasopressin content were equivalent in the two water-deprived groups, indicating similar hydrational status. It is concluded that the weight loss effect in water-deprived rats is due to excessive voluntary exercise, and that other factors that energize behavior should produce a similar effect.