Effects of small hypothalamic and preoptic area lesions on vaginal cyclicity, ovulation and ovarian weights of female rats were examined. Animals were then gonadectomized and tested for lordosis behavior following injections of estrogen alone and estrogen plus progesterone. Male sex behavior was also measured during daily treatment with testosterone. Relative to sham operated rats, lesions in the dorsal preoptic area produced a significant increase in lordosis behavior, virtual elimination of male sex behavior, and only marginal effects on ovarian function. Animals with lesions in the ventral preoptic area showed constant vaginal cornification, lack of ovulation and significantly smaller ovaries than the other groups. These rats also tended to show more female sex behavior and less male sex behavior than sham operated rats. Animals with lesions in the anterior hypothalamus and dorsomedial hypothalamus showed normal ovarian function and levels of female and male sex behavior comparable to the ventral preoptic lesioned rats. Animals with lesions in the ventromedial hypothalamus tended to show lower levels of lordosis behavior than sham animals but displayed a dramatic and significant increase in male copulatory behavior relative to the other groups. These data indicate a clear dissociation between the neural control of cyclic gonadotropin activity and sex specific reproductive behavior.