1. The actions of chicken and porcine secretins and vasoactive intestinal peptides (VIPs) were compared on the rate of flow and rate of protein secretion from the exocrine pancreas in urethane anaesthetized turkeys and rats. 2. Chicken VIP was about twice as potent as porcine VIP and 100-150 times as potent as chicken and porcine secretins in stimulating the flow of pancreatic juice in the turkey. 3. Porcine secretin was a strong stimulant of the flow of pancreatic juice in the rat, but chicken secretin and the two VIPs were only active in doses 20-50 times higher than those of porcine secretin. 4. Neither the two VIPs nor the two secretins significantly stimulated the rate of pancreatic protein secretion in the turkey or rat. 5. In the turkey I.V. infusion of graded doses of chicken VIP produced graded increases in the flow of pancreatic juice; in the presence of an infusion of a low dose of CCK8 the flow of juice secreted in response to the highest dose of chicken VIP was significantly lower compared with the infusion of VIP alone, and responses to the other doses of VIP were lower but not significantly so. The infusion of chicken secretin reduced the flow of juice in response to infusions of chicken VIP, but the differences were not significant. There was no significant difference in either the rate of flow, or rate of protein secretion from the turkey pancreas in response to an infusion of chicken secretin and CCK8, compared with CCK8 alone. 6. The results cast doubt on the importance of secretin for regulation of the avian pancreas, and suggest instead that VIP might have a physiological role in regulating the flow of pancreatic juice in birds.