The dopamine agonist, apomorphine, or its antagonist, haloperidol, was administered to rats whose drinking was induced by fixed-interval schedules of pellet delivery or by water deprivation. The first study revealed that both drugs produced dose-dependent decreases in bar-pressing and schedule-induced polydipsia (SIP). At higher doses, haloperidol also depressed the rate of pellet delivery. The second study demonstrated that the suppression in SIP obtained in the first study was primarily due to the direct effect of the drugs and not to changes they produced on the underlying food reinforcement schedule. The third study showed that both drugs suppressed water deprivation-induced drinking during a ten-minute session. Apomorphine delayed the onset of drinking, while haloperidol accelerated the cessation of drinking. The results indicated that apomorphine produced motor deficits that interfered with consummatory behavior, and that haloperidol interfered with the sensory feedback necessary to sustain consummatory behavior.