This trial is conducted in Europe. The purpose of this trial is to compare the pharmacokinetic properties (the exposure of the trial drug in the body) of different formulations of NN1218.

Inclusion Criteria:

• Type 1 diabetes mellitus for more than 12 months
• Treated with multiple daily insulin injections or continuous subcutaneous insulin infusion (CSII) for more than 12 months
• Body mass index (BMI) between 18.0-28.0 kg/m^2 (both inclusive)

Exclusion Criteria:

• Subjects 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