Plasma insulin responses to intragastric (i.g.) (1.5 g/kg b.wt.) and "isoglycemic" intravenous (i.v.) glucose were measured in ten unanesthetized young pigs to assess the contribution of gastrointestinal factors to the total insulin secretion as observed after i.g. glucose. The participation of nerves was estimated by comparing metabolic tests performed before and after total surgical pancreatic denervation. In the five animals which survived the procedure, 52.6% of the insulin response after i.g. glucose was calculated to be due to incretion factors, a value similar to the 54.8% found in the preoperative series (with intact pancreatic innervation). The response of IR-GIP to i.g. glucose was not significantly different between preoperative and postoperative tests, although a subtotal duodenectomy had to be performed in the course of the operation designed to completely denervate the pancreas. Intragastric and i.v. (also tested by bolus glucose injection) glucose tolerance was almost identical before and after the operation. It was concluded that nerves do not seem to play a major role in mediating the incretin effect in pigs. Hormonal factors, including GIP, appear to be more important.