The lordosis behavior in female rats following removal of the vomeronasal organ (VNO) was observed for a period of 14 hrs by means of a video camera monitor. Although the VNO-ablated female rats received a large number of mounts (96 to 204 times) by sexually active males, they showed only low scores (8 to 22) of lordosis quotients (number of lordosis behavior displayed/number of mounts X 100). In contrast, sham-operated females showed the highest lordosis quotients of 100 as was expected.