On night before the study starts, you will be asked to come to Masonic Clinical Research Unit (MCRU) after dinner (between 8-10 PM). Upon your arrival two catheters will be placed in the arms to establish intravenous access. One will be used for subsequent blood sampling and the other will be used for infusion. We will administer intravenous insulin as necessary to maintain blood glucose between 100-150 mg/dL overnight. Blood sugars will be obtained every 15-60 minutes overnight to ensure the glucose remains at target. At 7 AM the next morning, the intravenous insulin will be stopped. The study will the start when by giving you a dose of either 100 or 200 units of U-500 regular insulin subcutaneously in random order (like a flip of a coin). Since insulin drops the blood sugar, we will also be ready to start an intravenous infusion of glucose to maintain your blood sugars at 100 mg/dl. To keep your sugar at this target, blood will be collected every 15-60 minutes to measure blood sugar and the information will be used by the investigators to figure out how much glucose to give you. We will continue to measure blood glucose until you can maintain blood glucose without a glucose infusion for at least 10 hours or start to experience hyperglycemia (BG > 150 mg/dl) for two hours after discontinuation of the glucose infusion. At that point, the catheters will be removed and you will be discharged to home. During your stay at the MCRU, carbohydrate free meals will be provided starting at noon and continued at traditional mealtimes thereafter for the duration of the glucose infusion. Non-caloric decaffeinated beverages will be available as needed. At the completion of the study you will be told to resume your usual diabetes medications.