Low-dose insulin infusion has recently been used to treat ketoacidosis. We have prospectively compared patients with ketoacidosis either treated with insulin infusion at the rate of 6 units per hour or with high-dose, intermittent subcutaneously administered insulin, with emphasis placed on the hormonal responses. Basal glucagon, cortisol, and growth hormone levels were elevated in both groups. Cortisol and growth hormone levels did not fall with therapy in either group but glucagon levels fell in parallel with glucose levels in both groups. There was no difference in the time taken for glucose levels to fall below 250 mg/100 ml between groups. Whereas both methods of therapy appeared to be equally effective, low-dose infusion had the advantages of ease of administration, a predictable, relatively linear rate of fall of glucose levels, and ability to be stopped abruptly in the event of hypoglycemia.