This trial is conducted in Japan. The aim for this trial is to investigate the pharmacodynamics and pharmacokinetics of insulin detemir and insulin NPH in Japanese subjects with type 1 diabetes mellitus.

Inclusion Criteria:

• Type 1 diabetes mellitus
• HbA1c (glycosylated haemoglobin) maximum 9.0%
• Duration of diabetes at least 1 year
• Body Mass Index (BMI) maximum 25.0 kg/m^2

Exclusion Criteria:

• Recurrent severe hypoglycaemia
• Proliferative retinopathy or maculopathy requiring acute treatment as judged by the Investigator
• Impaired hepatic function
• Impaired renal function
• Cardiac problems
• Uncontrolled treated / untreated hypertension
• Hepatitis B surface antigen, Hepatitis C antibodies or HIV (human immunodeficiency virus) antibodies, positive
• Known or suspected allergy against the trial products or related products including the components
• Previous history of serious allergy or anaphylactic reaction
• Any disease or condition which the Investigator feel would interfere with the trial participation or evaluation of the results
• Severe late-phase diabetic complications including nephropathy
• Blood donation of more than 400 mL (inclusive) in total within the last 12 weeks or more than 200 mL (inclusive) in total within the last 3 weeks
• Known or suspected alcohol and illicit substance abuse or dependence
• Pregnancy, breast-feeding (within a year after labour) or the intention to become pregnant
• The receipt of any investigational drug within the last 12 weeks prior to this trial
• Current or anticipated treatment with systemic corticosteroids