This paper reports our experience with the successful simultaneous transplantation of kidney and fetal pancreatic islets in 46-year-old diabetic man. No detectable C-peptide level was noted and the end-stage nephropathy required hemodialysis. The cadaver kidney and two masses of 8-week-cultured fetal islets were grafted simultaneously. After revascularization of the kidney, the islet masses were placed under the kidney capsule. Following transplantation, islet function was demonstrated by a higher C-peptide level, which subsequently persisted. Twenty-four months after grafting, islet function was provoked by glucagon and glucose, which led to elevations in the C-peptide and insulin levels. The insulin requirement fell from 58 to 24 U/day during the post-transplant period of 24 months. The mean value of HbA1C (5.6% +/- 0.3%) indicated a constantly normal carbohydrate metabolism. Improvements in retinopathy were also noted. Three periods of kidney rejection were diagnosed, but these proved reversible with high-dose steroid treatment. The serum and urine beta-2-microglobulin levels correlated well with rejection and recovery. More than 2 years after grafting, kidney functions is in the normal range. On sonography, the transplanted islet masses were repeatedly clearly visible, and 24 months following transplantation the volume was twice the original one. The results indicate that simultaneous kidney and fetal pancreatic islet grafting is advantageous in end-stage nephropathy secondary to type I diabetes mellitus.