In order to investigate whether an increased gastrointestinal potentiation of glucose-induced insulin release might be involved in the enhanced insulin response to oral glucose in pregnancy, seven normal women were subjected to an oral glucose tolerance test (OGTT) and an IV glucose infusion test (IVGI) in the last trimester of pregnancy and again four to ten weeks post-partum. The amount of glucose administered intravenously was adjusted to obtain plasma glucose concentrations similar to those of the preceding OGTT. By this technique it was possible to quantitate the amount of insulin release attributable to gastrointestinal factors. Contrary to expectations, the results revealed that the gastrointestinal potentiation of insulin secretion was reduced by more than 75% in late pregnancy (p less than 0.05). The hyperinsulinaemia of pregnancy is therefore not explained by an increased activity of the entero-insular axis. Moreover the results confirm a substantially increased beta cell sensitivity to a glycaemic stimulus in pregnancy.