Two to four weeks later, you will be asked to once again hold oral or injectable non-insulin medicines used to treat diabetes for 1 week prior to the second part of the study and to avoid exercise 48 hours prior to the study. During this time you will be again asked to monitor your blood sugars and call the investigators for help in managing your sugars if they go outside of the target recommended by your doctor. On night before the second part of the study starts, you will be asked to come to Masonic Clinical Research Unit (MCRU) after dinner. Intravenous lines will again be placed, intravenous insulin will again be given overnight to keep your blood sugar between 100-150 mg/dl, and in the morning you will be given the dose of U500 regular insulin you did not receive during the first visit. Your blood sugar will then be maintained at 100 mg/dl by the infusion of glucose. We will continue to measure blood glucose every 15-60 minutes 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. You will be fed the same diet as during your first visit and will be told to resume your diabetes medications at the time we send you home.