We compared carotid sinus baroreflex control of endogenous plasma arginine vasopressin (AVP) in chronically prepared conscious and acutely prepared anesthetized dogs. The carotid sinuses of both conscious and pentobarbital-anesthetized dogs were isolated bilaterally and perfused at constant pressures. Carotid sinus pressure (CSP) was changed between 200 and 50 mmHg in 25-mmHg steps in intact conscious and anesthetized dogs. Similar runs were repeated after vagotomy. Mean arterial pressure (MAP) and heart rate (HR) were monitored. At each interval of CSP, blood was withdrawn for AVP analysis by radioimmunoassay. MAP responses to changes in CSP were not different in the four experimental groups. Both anesthesia and vagotomy increased the HR responses to changes in CSP. With vagi intact, AVP increased at high CSP in conscious but not in anesthetized dogs. After vagotomy, low CSP led to an increase in plasma AVP that did not differ between conscious and anesthetized dogs. The results suggest that the release of AVP is modulated by the action of the carotid baroreflex as a normal component of an integrated efferent response. The response is similar in conscious and pentobarbital-anesthetized dogs and is normally buffered by reflexes with vagal afferents.