Intravenous glucose tolerance tests (GTT) were performed in 13 metabolically healthy patients at the first and second day after abdominal surgery. GTT were carried out during an additional infusion of bradykinin (BK) (80 microgram/h) in six of these patients at the first day (group A) and in seven patients at the second day (group B). Furthermore, GTT were performed in six patients with chemical diabetes with and without BK-infusion. In addition, the effect of BK on blood glucose concentration in the postabsorptive state was investigated in nine maturity onset diabetics and in five healthy volunteers. As a control, another nine diabetics received physiological saline. In both groups of surgical patients BK improved glucose tolerance (k-values: group A without BK 1.03 +/- 0.12, with BK 1.31 +/- 0.07; group B without BK 0.85 +/- 0.18, with BK 1.25 +/- 0.21). This was also true in chemical diabetics (without BK 0.81 +/- 0.03, with BK 1.08 +/- 0.04). While BK did not change blood glucose concentration in healthy volunteers, it reduced that of diabetics by 12.2 +/- 1.4% continuously during 100 min. No spontaneous drop of blood glucose was observed in diabetics receiving saline. These results are in good accord with the present view that kinins may play a role within the regulation of carbohydrate metabolism.