Insulin secretion is partially regulated by hormonal and nervous signals arising from the duodenum. To ascertain the role of absorption through the villi on insulin secretion, the blood levels of immunoreactive insulin (IRI) in 13 normal children (T) were compared with those in 13 with flat jejunal mucosae (MJP). The bowel was stimulated by the infusion of Nutramigen direct into the duodenum at 4 ml/mn m2. In the control group (T) IRI increased from the 10th minute of the perfusion to reach a plateau after the first hour (256 +/- 107 pmol/l). In the MJP group the rise of IRI was delayed and the plateau lower (169 +/- 25 pmol/1) but the difference in the two groups was not statistically significant. During the first 10 minutes when there is no significant change in blood glucose levels IRI levels increased in the T group (p less than 0.01) but there was no significant change in the MJP group. These results suggest that when villi are intact stimulation of the duodenum causes insulin secretion; but when there are no villi, there is a delay in the secretion.