The nigrostriatal dopamine (DA) system is sexually dimorphic. In female but not male rats, striatal DA activity is modulated by gonadal steroid hormones. Ovariectomy (OVX) decreases striatal DA release and turnover. Estrogen replacement restores the response to that of the intact female in estrus. In contrast, castration (CAST) of male rats has no effect on the stimulated release of DA from striatal tissue. This report addresses the question: Does estrogen act directly on the striatum to induce changes in DA release? Physiological concentrations of 17 beta-estradiol and other steroids or a nonsteroidal estrogen analog were applied directly to striatal tissue maintained in an in vitro superfusion system. The effect of hormonal treatments on the responsiveness of striatal DA terminals to stimulation was examined in tissue from OVX females and intact and CAST male rats. The results are summarized as follows: (1) Infusion of 17 beta-estradiol (p less than 0.01) and diethylstilbestrol (p less than 0.05) increased amphetamine (AMPH)-stimulated striatal DA release from striatal tissue of OVX female rats compared with the effect of cholesterol. 17 alpha-Estradiol also tended to potentiate the striatal DA response to AMPH, but this result was not statistically significant (p less than 0.062). 17 beta-Estradiol had no effect on AMPH-stimulated DA release from striatal tissue of intact male rats. (2) The KCl-stimulated release of DA from striatal tissue of OVX rats exposed in vitro to 100 pg/ml 17 beta-estradiol (a physiological dose) was significantly greater (p less than 0.05) than the response after exposure to vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)