In rats exploring a symmetrical Y-maze, an acute injection of quinpirole or intermittent brief footshocks did not change the level of locomotion. The combined treatment of quinpirole and footshocks elicited an immediate locomotor stimulation. When the experimental session was repeated daily, there was a further increase of hyperlocomotion (i.e. sensitization). In parallel groups of rats treated with quinpirole and placed in the Y-maze daily without shock, or subjected only to daily footshock, locomotor activity did not increase. Footshock, therefore, has a synergistic effect in the development of sensitization to quinporole. When the dose-response relationships of quinpirole were compared between naive and sensitized animals, the magnitude of stimulation differed, but the threshold stimulant dose did not change. Pretreatment with sulpiride completely antagonized the hyperlocomotion in both drug-naive and quinpirole-sesitized rats. The results support a view that quinpirole facilitates the emergence of patterned motor behaviors. Non-contingent, brief footshock elicits running as the prepotent behavior in the Y-maze, and hastens the development of behavioral sensitization to quinpirole.