The influence of cervical vagotomy on the isoprenaline-induced renin and vasopressin release was investigated in rats. Plasma vasopressin levels were measured using a specific radioimmunoassay. Bilateral vagotomy enhanced the isoprenaline-provoked vasopressin release; however, the simultaneous increase in plasma renin concentration was diminished. This effect of bilateral vagotomy on renin release could be mimicked by i.v. infusion of vasopressin into rats whose vagi remained intact. On the other hand, in Brattleboro rats with vasopressin deficiency, bilateral vagotomy did not modify renin release. We conclude that, after bilateral vagotomy, isoprenaline elevated plasma vasopressin levels, which then attenuated the concurrent renin release, substantiating that endogenous vasopressin might participate in the control of renin release.