Androgen has a potency to induce female sexual behavior in ovariectomized rats. This study investigated the inhibitory effect of progesterone (P) on lordosis behavior facilitated by androgen. Ovariectomized female rats were given 100 to 800 micrograms/kg testosterone propionate (TP) or 5 micrograms/kg estradiol benzoate (EB). Forty-four hours after administration of the TP or the EB, all females received 0.5 mg P, and the first behavioral test was carried out four hours later. TP-treated animals showed lordosis responses in a dose dependent manner. Two weeks after the first test, the animals were retested by using the same hormonal regime as in the first test, except that an additional 5 mg P was administered 1 h prior to the TP or the EB. As a result, significant reductions in sexual receptivity were observed in the TP-treated as well as in the EB-treated females. These results indicate that progesterone can inhibit androgen-induced lordosis behavior in female rats.