Studies were conducted on dogs to test the efficacy of cyclosporin A (CyA) in prolonging normoglycaemia and graft survival after whole-organ pancreas allograft transplantation. Five dogs subjected to pancreatectomy alone served as controls. Withholding immunosuppression after transplantation (five animals) resulted in the same median duration of survival as occurred in the controls (13 days). Azathioprine and steroids (seven animals) produced median durations of normoglycaemia and survival of 9 and 23 days respectively. Animals given CyA 18 mg/kg/day (five) and 25 mg/kg/day (10), however, showed median durations of normoglycaemia of 18 and 55 days (p less than 0.05 and p less than 0.02) respectively and median survival times of 36 and 85 days (NS and p less than 0.02). If CyA proved effective in controlling rejection of pancreas allografts in man it would offer unstable diabetics in renal failure a more hopeful outlook than conventional immunosuppression.