In a patient with phaeochromocytoma who presented with unstable diabetes mellitus, an artificial endocrine pancreas was used intraoperatively. Anaesthetic agents included enflurane, nitrous oxide and oxygen. Nicardipine was used to control hypertensive episodes. The initial blood glucose concentration was 173 mg X dl-1 and it decreased to 110 mg X dl-1 in response to insulin infusion, but plasma catecholamines were markedly increased. Seventy minutes later, the glucose concentration increased progressively to 249 mg X dl-1 despite massive insulin infusion, maximally 5.64 mU X kg-1 X min-1. The blood glucose concentration reached a peak at the time of the ligation of the venous drainage from the tumour and the peak was coincident with that of plasma catecholamine levels (epinephrine: 20.8 ng X ml-1, norepinephrine 16.4 ng X ml-1). Both glucose and catecholamine concentrations decreased promptly after removal of the tumour and hypotension followed likely because of a persistent vasodilatatory effect of nicardipine. The profiles of blood glucose, insulin and glucose infusion rates provided by the artificial endocrine pancreas suggested that the insulin resistance began to be reversed shortly after removal of the phaeochromocytoma.