This trial was conducted in Europe. The aim of this trial was to compare the pharmacodynamic (the effect of the investigated drug on the body) response of insulin degludec (insulin 454) with insulin glargine at steady-state conditions in subjects with type 1 diabetes mellitus.

Inclusion Criteria:

• Type 1 diabetes mellitus (as diagnosed clinically) and treated with insulin for at least 12 months
• Subject is considered to be generally healthy, except for the underlying diabetes mellitus and related morbidity (such as well controlled hypertension and dyslipidaemia) based on an assessment of medical history, physical examination and clinical laboratory data, as judged by the Investigator
• Body Mass Index (BMI) between 18.0 and 28.0 kg/m^2 (both inclusive)
• Glycosylated haemoglobin (HbA1c) below or equal to 10.0 % based on central laboratory results
• Subject with a daily basal insulin requirement of between 0.2 IU/kg/day and 0.6 IU/kg/day will be allowed to participate in the trial. Current total daily treatment with insulin must be less than 1.2 U/kg/day

Exclusion Criteria:

• Known or suspected allergy to trial product(s) or related products
• Subject who has participated in any other trials involving investigational products within 3 months preceding the start of dosing
• Subject who has donated any blood or plasma in the past month or in excess of 500 mL within the 12 weeks preceding screening