Continuous intravenous infusion of small amounts of insulin has been used in the management of a series of patients with diabetic ketoacidosis. In 13 patients with a plasma glucose level on admission of 725 mg/100 ml (+/- 80 S.E. of mean) and an arterial pH of 7.07 +/- 0.05 a mean loading dose of 6.5 +/- 0.82 units of soluble insulin was administered intravenously, and thereafter a sustaining infusion of 6.5 +/- 0.82 U/hr was continued until ketosis was corrected and the plasma glucose fell below 300 mg/100 ml. The total insulin dose needed to achieve this was 39.2 +/- 6.6 units given over a 3 to 10-hour period. Plasma insulin was measured in patients who had not previously received insulin and the mean level at an infusion rate of 4 U/hr was 75.6 +/- 8.0 muU/ml. Plasma glucose fell at a regular rate of 101 +/- 11 mg/100 ml/hr, and ketosis improved in parallel. Plasma potassium was well maintained throughout treatment. This regimen of treatment was clinically effective and simple to follow.