This trial is conducted in Europe. The aim of this trial is to investigate the pharmacodynamic response (the effect of the investigated drug on the body) of insulin degludec/insulin aspart (IDegAsp) at steady state in subjects with type 1 diabetes.

Inclusion Criteria:

• Type 1 diabetes mellitus (as diagnosed clinically) for at least 12 months
• Treated with multiple daily insulin injections or continuous subcutaneous insulin infusion (CSII) for at least 12 months
• Body mass index (BMI) 18.0-28.0 kg/m^2 (both inclusive)
• Glycosylated haemoglobin (HbA1c) maximum 9.5 %
• Fasting C-peptide maximum 0.3 nmol/L

Exclusion Criteria:

• Smoker (defined as a subject who is smoking more than 5 cigarettes or the equivalent per day)
• Not able or willing to refrain from smoking, use of nicotine gum or transdermal nicotine patches during the inpatient period
• Subject who has donated any blood or plasma in the past month or more than 500 mL within 3 months prior to screening
• Surgery or trauma with significant blood loss (more than 500 mL) within the last 3 months prior to screening