This trial is conducted in the United States of America (USA). The aim of the trial is to compare the exposure of two formulations of insulin degludec/insulin aspart (NN5401) in healthy subjects.

Inclusion Criteria:

• Considered generally healthy upon completion of medical history, physical examination, vital signs and electrocardiogram (ECG), as judged by the physician
• Body mass index between 18.0 and 27.0 kg/m^2 (both inclusive)

Exclusion Criteria:

• Subject who has donated any blood or plasma in the past month or more than 500 mL within 3 months prior to trial start
• 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 and use of nicotine gum or transdermal nicotine patches during the inpatient period