In order to elucidate the role of the vagus nerve in the intestinal phase of pancreatic polypeptide (PP) release, mongrel dogs were given a 4-min intraduodenal infusion of saline, 20% glucose, or 10% soybean oil solution (50 ml each), before and one month after truncal vagotomy including pyloroplasty (TV). The saline infusion did not change the basal PP level, while the glucose infusion elicited a monophasic transient PP release, and the soybean oil infusion elicited a monophasic prolonged PP release in the intact dogs. The PP response following glucose infusion was almost abolished after TV, while the PP response to fat was attenuated, but a significant increase was nevertheless observed after TV. These results suggest that the vagus nerve has an important role in the intestinal phase of PP release and that other factors, e.g. hormonal, might also be involved in the regulatory mechanism, especially after fat loading.