A program using continuously pumped IVI [intravenous insulin] was devised to restore glycemia of unstable diabetes under ambulatory, fed conditions to that of nondiabetic subjects. Five patients with unstable diabetes were studied. The daily regimen consisted of 4 meals of equal carbohydrate, fat and protein content taken at 8 a.m., 2 p.m., 8 p.m. and 2 a.m. and 1 h of standardized exercise in the 2nd postprandial hour (except after the 2 a.m. meal). Confirmation of physiologic replacement of insulin by the IVI program was possible because 4 patients had low insulin-binding antibodies and minimal distortion of serum IRI [immunoreactive Best glucose control was achieved by increasing the basal flow rate (mean, 0.15 mU[milliunits]/kg per min) 10-fold from 15-60 min after daytime meals and from 15-105 min after the 2 a.m. meal and doubling the basal rate overnight. Contrasted to the results with SCI [subcutaneous insulin] the IVI program significantly improved the mean blood glucose and mean amplitude of glycemic excursions. The IVI program restored the time to glucose peak and postprandial baseline glucose recovery to normal; the amplitude of glucose increase to peak remained somewhat greater than normal.