Six normal subjects were studied to investigate the mechanisms involved in the release of immunoreactive beta-endorphin (ir-beta EP) in response to insulin hypoglycaemia. Insulin alone (0.2 U/kg body weight) was followed after a 30 min lag period by a congruent to 2.5 fold elevation of plasma ir-beta EP, with a return to basal levels by 90 min. Concurrent infusion of 10% dextrose at 250 ml/h for 2 h prevented the increase in plasma ir-beta EP levels, suggesting an effect of hypoglycaemia rather than a direct effect of insulin. Premedication with atropine 0.6 mg at -30 min was followed by hypoglycaemia equivalent to that seen with insulin alone, but no increase in plasma ir-beta EP, suggesting the involvement of cholinergic mechanisms in the neural mediation of ir-beta EP release in response to hypoglycaemia.