Patients with severe diabetic ketoacidosis (pH less than 7.10) were treated according to two protocols. Protocol I consisted of high-dose insulin therapy by intravenous and intramuscular injections and bicarbonate infusion and was used in the first 12 patients; they received an average of 260 U insulin and 167 mmol bicarbonate in the first 6 h of treatment. Protocol II consisted of low-dose continuous intravenous insulin therapy, 8 U/hour, without bicarbonate in a further 12 patients. Rehydration and potassium-supplementation were the same in both methods. Basal data of both groups were not significantly different. The fall of plasma glucose concentration, rise in arterial pH and decrease in 3-hydroxybutyrate were similar in the two groups. The mean time to achieve a pH equal to or greater than 7.30 was 6.8 hours in the high-dose group and 7.6 hours in the low-dose group (p greater than 0.10). Potassium supplementation and potassium concentration during both treatments were the same. During the low-dose treatment the mean (+/- SD) plasma insulin concentration was 121 +/- 46 microU/ml. The presence of insulin binding antibodies did not result in lower free insulin concentrations. Thus, in the treatment of severe ketoacidosis continuous intravenous therapy with low-dose insulin is as effective as high-dose therapy and bicarbonate-administration is probably unnecessary.