To determine the neuroendocrine pattern of response to excessive drinking induced by exposure of rats to an intermittent distribution of food (schedule-induced polydipsia, SIP), the present experiment investigated changes in plasma corticosterone, prolactin and catecholamines in chronically catheterized rats that had developed or not this form of adjunctive behaviour. It was found that rats that engage in excessive drinking displayed decreased plasma levels of corticosterone and increased levels of prolactin during the course of a SIP session. There was, however, no differences between groups in plasma catecholamine levels. The differences observed between SIP-pos and SIP-neg rats were entirely condition-specific, since they disappeared in the absence of access to water.