36 patients in severe diabetic ketoacidosis were studied prospectively. All patients were treated with small doses of insulin, the first 18 by the intramuscular route and the remainder by continuous intravenous infusion. These patients were compared with 25 ketoacidotic patients who were treated with large intravenous boluses of insulin. With the intramuscular regimen there was a slower fall of blood-sugar than with intravenous insulin administered either in boluses or as a continuous infusion. The acidosis took longer to correct when small doses of insulin were used. In practice a long time interval between correction of the hyperglycaemia and correction of the acidosis may be a problem when the continuous infusion of insulin is used. Potassium requirements during treatment were identical (30-40 mmol/l fluid infused) and independent of the insulin regimen. However, small doses of insulin led to a poor retention of potassium. In the management of diabetic ketoacidosis the mode of administration of insulin is of limited significance, and small doses, although effective in most cases, are not clearly superior to conventional treatment with large doses.