The effect of sham feeding on glucose metabolism was studied in eleven normal subjects. At random, one intravenous glucose tolerance test (25 g glucose/4 min) was preceded by 15 minutes of pure sham feeding (the sight and smell of a meal but not the taste) which continued for the first 15 minutes after the intravenous glucose load. Pancreatic polypeptide increased significantly during sham feeding and decreased significantly in response to the glucose injection. The glucose disappearance rate was significantly improved from 1.56 +/- 0.22 to 2.07 +/- 0.33 min-1 when the glucose tolerance test was preceded by sham feeding (p = 0.02). Incremental areas of plasma insulin, plasma C-peptide, and insulin secretion rates were not significantly influenced by sham feeding. We conclude that sham feeding by the sight and smell of food improves glucose tolerance in normal subjects without alteration in insulin secretion.