The effects of bilateral cut of the stria terminalis (ST) on the dosage of estradiol benzoate (EB) needed to induce the lordosis reflex in the ovariectomized female rat were examined. Seven different doses ranging 0.5-20 microg were given s.c. in oil, daily for 2 days In counterbalanced order, at 3-week intervals. The log dose-response relationship was linear in both ST-cut and sham-operated control rats. A significantly larger dose of 9.3 + 1.4 (mean+-SEM) microg/day of EB was needed in the ST-cut rats (n=8) to obtain a 50% lordosis quotient than in the controls (n=7), in which a 2.0+-0.3 microg/day dose had a similar effect. The slope of the dose-effect curve was significantly steeper in the ST-cut rats than in the controls. The ST mediates facilitatory effects of estrogen on the lordosis reflex that originate presumably in the amygdala.