Counterregulatory hormones and hypoglycaemic symptoms were studied during a gradual decline in plasma glucose in a 66-year-old man before and 9 weeks after removal of an insulin-producing tumour. Before surgery the adrenaline started to respond first at plasma glucose 2.8 mmol l-1. He reported no autonomic symptoms although plasma glucose fell to 2.3 mmol l-1 with a corresponding adrenaline rise to 4.64 nmol l-1. After surgery adrenaline responded at a plasma glucose of 3.7 mmol l-1 and he started to sweat and tremble at a plasma glucose of 3.1 mmol l-1 (corresponding adrenaline 2.63 nmol l-1). The lack of autonomic symptoms preoperatively may indicate adrenaline insensitivity, possibly as a result of repeated hypoglycaemia.