β‐Adrenergic sensitivity and counterregulatory hormone and symptomatic responses to hypoglycaemia were studied in a 22‐year‐old man before and 3 and 34 weeks after removal of an insulinoma. The β‐adrenergic sensitivity was measured by the effect of an isoprenaline infusion on the heart rate, and the dose needed to increase the heart rate by 25 beats min−1 (I25) calculated from regression lines. The glucose thresholds for the hormonal responses and symptoms were studied during a gradual fall in plasma glucose using a hypoglycaemic clamp technique. As compared with preoperative values, β‐adrenergic sensitivity was unchanged 3 weeks after surgery, but showed a marked improvement after 34 weeks, the I25 (in μg isoprenaline) being 0.96, 0.86, and 0.56, respectively. The hormone responses to hypoglycaemia were earlier, but with no improvement in symptom generation at 3 weeks. After 34 weeks, the thresholds for both hormone release and symptom generation occurred at a plasma glucose approximately 1 mmol l−1 higher than before surgery. Thus, in our patient, there was a marked improvement in β‐adrenergic sensitivity, an earlier release of counterregulatory hormones, and an earlier recognition of hypoglycaemic symptoms after surgery. However, the restoration of these responses took more than 3 weeks. © 1997 John Wiley & Sons, Ltd.