The aims of this study were to determine the change in the rate of insulin-stimulated glucose disposal (insulin sensitivity) and the ability of insulin to inhibit its own secretion in four pancreas-kidney transplant recipients with insulin-dependent diabetes mellitus. Insulin sensitivity (glucose infusion rate, GIR) was measured by a euglycemic hyperinsulinemic clamp technique before and 2, 6 and 12 months after transplantation. The GIR values in the four recipients were normalized within 2 months and remained normal for 12 months after transplantation, despite long-term steroid therapy for immunosuppression. Physiological hyperinsulinemia (50-70 μU/ml) suppressed plasma C-peptide, but its nadirs were still higher than the basal levels in normal controls. Taking into account evidence of a minimal increase in the concentration of circulating insulin that inhibits insulin secretion in healthy subjects and evidence of increased insulin secretion in pancreas recipients, the authors speculate that defective feedback inhibition of insulin secretion could contribute, at least in part, to the disproportionate basal hyperinsulinemia in patients with a denervated, transplanted pancreas in the absence of insulin resistance.