Female albino rats trained to press a bar to turn off a bright light while water-satiated performed better than rats trained while thirsty. It is suggested that thirst elicits responses such as increased activity which compete with stationary behavior required for bar-pressing. Since the proposed competing responses may facilitate locomotor behavior, this hypothesis might also explain the general finding that hunger or thirst facilitates performance on tasks where escape or avoidance requires locomotion. Switching satiated subjects to the thirsty condition caused decreased performance, while the opposite shift apparently failed to improve performance above the level of a control group.