Type 1 diabetes mellitus (also called juvenile diabetes) occurs when the pancreas stops making insulin. Insulin helps the body use the energy in foods. Without insulin, blood levels of sugar become high. Over time, high blood sugar levels can lead to blindness, kidney failure, damage to nerves, and heart disease. To keep blood sugar levels in the normal range, people with type 1 diabetes must inject insulin several times each day and follow a special diet. There are several types of insulin. Short-acting (regular or lispro) insulins begin to act soon after injection. Long-acting (neutral protamine Hagedorn [NPH], lente, ultralente, or glargine) insulins do not begin to act until several hours after injection, but then they continue to act for many hours. For example, a dinnertime injection of long-acting insulin controls sugar levels throughout the night. A very low blood sugar level (hypoglycemia) is a dangerous complication of insulin treatment. To avoid hypoglycemia during the night, doctors often tell patients to “split” their evening insulin dose by taking short-acting insulin at dinner and long-acting insulin at bedtime instead of taking both forms of insulin at dinnertime (“mixing”). However, nobody has done a careful study to see whether “splitting” is truly better than “mixing” the evening insulin.