Differences were observed in the ovulation rates of the right and left ovaries in response to unilateral lesions of the cervico-vaginal plexus (CVP) followed by pseudopregnancy or by anaesthesia of the CVP induced with panthocaine plus adrenaline (right ovary 6·7±0·4 (s.e.m.) vs left ovary 4·6 ± 0·9; P<0·05). Pseudopregnancy (days showing a dioestrous smear after copulation with a vasectomized male before an oestrous smear following a pro-oestrous one) lasted longer in rats with a lesion in the CVP than in a control pseudopregnant group (14·9 ± 0·5 vs 11·2 ± 0·5; P < 0·01). Anaesthesia of the CVP performed on each day of the oestrous cycle did not modify the ovulation rate compared with laparotomized animals. Both laparotomy and anaesthesia of the CVP performed on oestrus or day 1 of dioestrus blocked ovulation but when they were performed on day 2 of dioestrus or pro-oestrus they failed to do so (laparotomy 9/18 vs 12/14, P<0·05; anaesthesia of CVP 3/11 vs 17/17, P < 0·05). The number of ova shed by the left ovary in animals with anaesthetized CVP was lower than by the right ovary (4·5 ± 0·6 vs 6·2 ± 0·5; P<0·05). These results add further support to the idea that the CVP participates in the regulation of ovulation rate, and that the left ovary is less adaptable than the right when innervation is challenged.