The effect of chlordecone on behavioral estrus was examined in adult ovariectomized female rats. Chlordecone has been reported to resemble estrogen in altering pituitary secretions, in producing vaginal cornification, in increasing uterine weight and in competing for binding to the estrogen receptor. In the present study, 10, 25, 50 or 75 mg/kg chlordecone was substituted for estrogen in the estrogen-progesterone priming sequence used to facilitate sexual behavior of ovariectomized female rats. Sexual receptivity was measured by the number of lordosis responses exhibited by the female when mounted by a sexually active male. Chlordecone failed to substitute for estradiol in producing lordosis behavior. When female rats were given chlordecone in addition to estrogen plus progesterone, chlordecone reduced the lordosis behavior usually seen in these steroid primed animals. In further studies, chlordecone's effect on the CNS progesterone receptor was examined. Unlike estradiol, chlordecone did not induce progesterone receptors. Furthermore, chlordecone attenuated the increase in progesterone receptors seen after estradiol treatment. These findings suggest that chlordecone fails to mimic, and may actually interfere with, estrogen's facilitative effects on neurally mediated reproductive events.