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.

Inclusion Criteria:

• Type 1 diabetes mellitus treated with insulin four times daily (basal bolus treatment) at least three months before screening.
• AGe: 18-60 years
• BMI: 18-27.5
• No nefro- or neuropathy; i.e. S-creatinin below 120 μmol/l and normal monofilament examination
• Written informed consent

Exclusion Criteria:

• Pregnant women or patients planning to become pregnant during the investigation period
• Reduced eyesight; i.e. visus > 0.3 evaluated at the latest eye exam.
• Patient lacking the ability to sens insulin sensitivity
• Serious rival disease, i.e. heart disease, severe liver or lung impairment, severe psychiatric disease.
• Suspicion of abuse or non-compliance
• Participation in another clinical trial