Chronic administration of an estrogenic agent is well known to attenuate the drinking response of rats to treatment with a variety of dipsogenic agents, and to increase plasma concentration of prolactin. Treatment with prolactin is also known to reduce the drinking response to administration of the dipsogenic agent, isoproterenol. Hence, a possibility existed that the antidipsogenic effect of chronic treatment with estrogen was mediated by an increased plasma prolactin concentration. Since bromocriptine, a dopaminergic agonist, is known to reduce plasma prolactin concentration in estrogen-treated rats, it was administered (1.0 mg/kg, IP) 15 min prior to treatment with either isoproterenol (25 micrograms/kg, SC) or angiotensin II (200 micrograms/kg, SC). The results suggest that the antidipsogenic effect of chronic treatment of rats with estradiol benzoate (30.4 and 45.7 micrograms/kg/day) can be reversed, at least partially, by acute administration of bromocriptine.