The plasma concentrations of gastrin, gastric inhibitory polypeptide (GIP), gut glucagon-like-immunoreactivity (gut GLI), insulin, glucagon, and pancreatic polypeptide (PP) were studied following the ingestion of a protein rich meal in late pregnancy and postpartum in 11 normal women. In pregnancy, the fasting plasma concentrations of glucose (mean +/- SEM in pregnancy: 4.1 +/- 0.1 mmol l-1, postpartum: 4.7 +/- 0.1 mmol l-1, P less than 0.01), gut GLI (25 +/- 3 v. 33 +/- 2 pmol-eqv l-1, P less than 0.01), and PP (7.9 +/- 1.0 v. 13.0 +/- 1.2 pmol l-1, P less than 0.01) were decreased, gastrin and GIP unaltered, and insulin (90 +/- 9 v. 72 +/- 5 pmol l-1, P less than 0.05) and glucagon (17 +/- 1 v. 13 +/- 1 pmol l-1, P less than 0.01) increased. The gastrin, GIP and glucagon responses to the meal were unaffected by pregnancy, whereas the responses of gut GLI (integrated responses in pregnancy: 1217 +/- 325 pmol-eqv l-1, postpartum 2223 +/- 404 pmol-eqv l-1, P less than 0.05) and PP (9801 +/- 1440 v. 14,078 +/- 1543 pmol l-1, P less than 0.01) were impaired and the insulin response enhanced (27,973 +/- 6814 v. 11,409 +/- 3102 pmol l-1, P less than 0.01) in pregnancy. The physiological implications of these findings are at present not known in detail. They may, however, be important for the altered carbohydrate metabolism in pregnancy and also for the changes occurring during gestation in gastrointestinal physiology.