Regular insulin was infused from one to five days in seven adult diabetic volunteers previously treated with subcutaneous insulin three times a day. Through a catheter inserted in a peripheral vein, a small pump delivered 66 ± 10 units of insulin per day in a 131.0 ± 4.0 ml. solution at mean rates of 26 ± 4 mU./min. between meals and 373 ± 58 mU/min. during meals; 40 per cent of the total daily dose was given during the three meal periods. These rates were precalculated. Patients were ambulatory. Blood glucose was assayed every fifteen minutes for eight hours during the postprandial periods and hourly otherwise. The over-all highest mean values were observed ninety minutes after breakfast (138 ± 17 mg./100 ml.) and four hours after dinner (121 ± 18); the lowest were 73 ± 7, 64 ± 7, 72 ± 15 at the end of the three high concentration insulin infusion periods and 56 ± 7 at 6 a.m. During insulin infusions the mean values of blood glucose parameters were as follows: 89 ± 7 mg./100 ml. for the mean blood glucose level; 66 ± 9 for the mean amplitude of glycemic excursion; and 17 ± 5 for the modified Schlichtkrull's M coefficient. Insulin infusions gave significantly lower blood glucose levels during the night and at breakfast than insulin three times a day, and higher blood glucose values before lunch. Both technics gave very good control of diabetes. Insulin infusions without blood glucose monitoring are feasible for several days in ambulatory patients.