The effects of abdominal vagotomy at proestrus on ovarian weight and antral follicles greater than 150 µm diameter and on serum levels of gonadotropins and testosterone were assessed 24 and 48 h and 4 and 8 days after surgery. Serum levels of estradiol were assessed at 4 and 8 days. Vagotomy (1) increased ovarian weight at 48 h, decreased ovarian weight at 4 days, but had no effect by day 8. (2) Vagotomy increased healthy antral follicles 151–394 µm diameter at 24 and 48 h and increased atresia in this size range at 4 and 8 days. (3) Vagotomy decreased healthy follicles 151–394 µm at day 8. (4) Vagotomy decreased healthy follicles 395–570 µm at 24 h and decreased atretic follicles at 48 h. (5) Vagotomy decreased the largest (over 570 µm diameter) healthy follicles at 24 h and 8 days. (6) Vagotomy decreased basal serum LH levels at 48 h and 8 days. (In contrast, vagotomy increased FSH at 24 h). There was no effect on blood levels of estradiol and testosterone. These findings are discussed in relation to the hypothesis that the vagus nerve is a component of the hypothalamohy-pophyseal-ov