The effects of lesions of the anterior hypothalamus and preoptic area on mating behavior, estrous cyclicity and ovulation in the female rat were evaluated. (1) Significant levels of mating behavior occurred after ovariectomy, during vaginal diestrus, in 4 8 animals with lesions of the anterior hypothalamus, and in 2 8 animals with lesions of the preoptic area. (2) The anterior hypothalamic and preoptic area lesioned groups showed more mating behavior than the respective sham groups following injection of the lowest dose of estrogen. (3) Lesions of the anterior hypothalamus failed to reduce mating behavior on days of proestrus, and increased mating on days of estrus compared with sham-anterior hypothalamic lesions. (4) Lesions of the preoptic area reduced mating behavior on days of proestrus, but increased mating on days of estrus compared with sham-preoptic area lesions (5) Lesions of the anterior hypothalamus, and shamlesions of the anterior hypothalamus or preoptic area did not disrupt estrous cycles, or reduce the number of tubal ova present on a morning of estrus. (6) Lesions of the preoptic area were more likely to disrupt cyclicity; they prolonged vaginal estrus in 3 8 animals, and prevented ovulation and development of pseudopregnancy in 4 8 animals. (7) The data suggest that lesions of the anterior hypothalamus interfered with inhibitory influences on mating without disrupting estrous cycles or ovulation. (8) Lesions of the preoptic area interfered with both facilitatory and inhibitory influences on mating behavior, and were more likely to disrupt estrous cycles, ovulation and the development of pseudopregnancy.