The effects of amphetamine, phencyclidine, dopaminergic blockers and atypical neuroleptics on the acquisition of schedule-induced polydipsia in rats were compared in a chronic dose regime followed by 7 days of withdrawal. All compounds suppressed water intake. However, different mechanisms were responsible. The antidopaminergic compounds inhibited the initiation of drinking, as the temporal pattern of licking was shifted to the right. Phencyclidine inhibited the maintenance of drinking as the number of licks/ml water consumed war; increased. The suppressing effect of amphetamine may have been due to the reduction of high rates of licking and/or a competition between licking and locomotor or other amphetamine-induced activities. The number of panel entries were increased by amphetamine and phenryclidine. The typical antidopaminergic compounds decreased the number of panel pushes, whereas the atypical antidopaminergic compounds were without effect on this parameter. In conclusion, it was possible to differentiate between the types of compounds investigated by comparing their effects on water intake, panel pressing, drinking efficiency and the temporal patterns of licking and panel pressing.