The effect of burn injury on blood sugar levels, serum insulin levels and glucose tolerance was studied in male rats. In the burned group (following 50 per cent surface burn injury), the blood sugar level was significantly increased after burn injury in comparison with control uninjured rats. Hyperglycaemia was blocked by injection of phentolamine (10 mg/kg) for 24 h or propranolol (50 micrograms/kg) 30 min before burn or if the animals were adrenalectomized 4 days before injury. Serum insulin levels were significantly decreased in the scalded rats and their glucose tolerance was impaired. Early hyperglycaemia probably arises as a result of adrenal medullary hyperactivity. The initial rise in blood glucose probably arises from glycogen breakdown, followed later by increased hepatic production of glucose. The 50 per cent body surface scald injury is followed, acutely, by a period of glucose intolerance. In part, this intolerance may be due to decreased serum levels of insulin. The inadequate response of insulin secretion in response to glucose loading may be due to inhibition of insulin secretion by pancreatic beta cells caused by elevated catecholamine levels, possibly in combination with the action of antagonists such as glucagon, which may be secreted in excess as a result of stimulation by catecholamines.