The mechanisms underlying the differences in uterotrophic potency between 2- and 4-hydroxyestrogens were explored. Doses of estradiol (E2)(10 micrograms/kg), 2-OHE2 (500 micrograms/kg) and 4-OHE2 (100 micrograms/kg) sufficient to induce near maximal cell nuclear estrogen receptor (ERn) binding were injected subcutaneously into 26 day old female rats. Uterine ERn concentrations declined more rapidly after 2-OHE2 than after E2 or 4-OHE2. E2 and 4-OHE2 both elicited a significant increase in uterine wet weight, measured at 24-36 hrs after injection. 2-OHE2 had no significant effect and neither synergized with nor antagonized the effects of simultaneously administered E2 or 4-OHE2. Under in vitro conditions at 25 degrees C, 2-hydroxyestrone (2-OHE1) and 2-OHE2 both dissociated from the receptors more rapidly than either their parent monophenolic estrogens or the corresponding 4-hydroxyestrogens. These results suggest that differences in estrogenic potency between 2- and 4-hydroxyestrogens may partly be a function of the dissociation kinetics of their estrogen receptor complexes.