Ovariectomized rats were treated for 2 weeks with 17 beta-estradiol (0.0002-100 micrograms/day). [3H]spiperone striatal dopamine receptor binding was maximally increased by 30% after 0.05 micrograms/day of 17 beta-estradiol and a similar increase is observed at higher doses. By contrast, plasma prolactin concentrations of these rats are unchanged after 0.05 micrograms/day and increased after 100 micrograms/day. A chronic estradiol treatment at very low doses (0.0002-0.001 microgram/day) leads to increases in pituitary dopamine receptor binding while plasma prolactin levels are unchanged. At higher doses (1-100 micrograms/day) binding is decreased and plasma prolactin concentrations are elevated. [3H]spiperone striatal dopamine receptor binding is elevated in lactating female rats compared to intact or ovariectomized female rats. Anterior pituitary dopamine receptor concentrations fluctuate during the estrous cycle while striatal dopamine receptors are unchanged. An injection of 30 ng of estradiol, which reproduces the estradiol proestrus surge, leads as in proestrus, to a decrease of anterior pituitary dopamine receptors.