Rats were vagotomized at proestrus and 4 days later serum prolactin and progesterone were determined by radioimmunoassay. The histology of the ovaries and the activity of ovarian Δ<sup>5–</sup>3β-hydroxysteroid dehydrogenase (3β-HSD) were also studied. There was no difference between hormone values in sham and vagotomized rats 4 days after surgery. In addition, the ovarian histology and activity of 3β-HSD were similar in both sham and vagotomized animals. We conclude that vagotomy at proestrus does not interrupt estrous cycles by activating the corpus luteum.