The effects of small lesions in the preoptic area (POA) of female rats on estrous cycles, LH responsiveness, and receptivity were studied. Regularly cycling rats received lesions confined to either the periventricular portion or the ventral portion of the rostral preoptic area, or a combination of these two sites. Nine animals showed persistent vaginal cornification (PVC) following lesion placement. All of these had lesions in the periventricular preoptic area. In contrast, five of six animals which showed repeated periods of pseudopregnancy (RPP) had lesions in the most ventral portion of the preoptic area. Lesions which damaged both the periventricular POA and the ventral POA gave mixed results. Following ovariectomy and estrogen and progesterone stimulation, the RPP animals had higher levels of LH 6 hr after the P injection than did the control animals or PVC animals. In three different tests for female sexual behavior--with estrogen alone, estrogen plus progesterone, and low estrogen priming and repetitive sexual stimulation--the PVC animals had consistently lower receptivity than the controls. The RPP animals were more receptive than the controls in all but the estrogen plus progesterone tests. The decreased levels of receptivity of the PVC animals could be related to a disruption of the LHRH system, while the RPP group responses could reflect a hypersensitivity of remaining neurons to estrogen.