A series of experiments was undertaken to examine the role of the vagus nerve in body weight regulation and the control of ingestive behavior in Syrian hamsters. Body weight, food and water intake, and feeding responsiveness to the putative satiety hormone cholecystokinin (CCK) were studied in hamsters with total subdiaphragmatic or selective gastric vagotomy. Body weight and food intake during ad libitum feeding were unaffected by either type of vagotomy. However, hamsters with total subdiaphragmatic or gastric vagotomy could better maintain body weight during intermittent food access. Vagotomy blocked feeding suppression after low-dose (4.0 micrograms/kg) systemic injections of CCK octapeptide (CCK-8). This blocking effect was specific to feeding suppression in response to CCK-8, because vagotomized hamsters remained responsive to other putative satiety hormones (bombesin, calcitonin, and thyrotropin-releasing hormone). Hamsters with either type of vagotomy were, however, responsive to high doses (greater than or equal to 8.0 micrograms/kg) of CCK-8, thus indicating that extravagal (possibly central nervous system) sites of CCK action may also be relevant to the control of feeding. The results are discussed in relation to normal vagal function in hamsters and vagal control of ingestive behavior in other species.