The main purpose of the study is to investigate the reason for the reduced number of hypoglycaemic attacks in type 1 diabetic patients when, for a period of time, using Insulin Aspart at meals together with NPH insulin mornings and evenings, and when, in another period of time, using human fast-working insulin at meals and NPH insulin mornings and evenings, and when the patients in both periods simultaneously take extra insulin at meals if high blood glucose values are found before meals.