Abstract Female rats were ovariectomized and given either 0.75, 3, 15 or 333 μg of estradiol benzoate (EB) subcutaneously. At varying times after EB injection, progesterone (P) was injected. Four to 6 hr after P injection, the females were tested for sexual receptivity with a male. The latency to exhibit lordosis was not affected by the level of exogenous EB. The length of time that the females remained sexually receptive was related to the level of exogenous EB.