Each subject will be randomly allocated to a sequence of two treatments applied at two separate dosing visits. At each dosing visit subjects will be injected with individualised doses of either BioChaperone® Combo or Humalog® Mix 25 immediately before ingesting a standardised mixed meal [(t=0 min) start of the meal]. Insulin doses will be identical at both dosing visits of one individual and will be administered subcutaneously in the abdominal region. Subjects will be asked to consume a standardised meal (e.g. pizza) for dinner at home in the evening before each dosing visit. Subjects will attend the clinical site in a fasted state in the morning of each dosing day and stay at the clinical trial centre until 10-hour after dosing (standardised test-meal procedure has been terminated after 6h). The two dosing visits will be separated by a wash-out period of 5-15 days.

Inclusion Criteria:

• Type 1 diabetes mellitus (as diagnosed clinically) >= 12 months.
• Treated with multiple daily insulin injections or CSII >= 12 months.
• Current total daily insulin treatment < 1.2 (I)U/kg/day.
• Current total daily bolus insulin treatment < 0.7 (I)U/kg/day.
• Usual Insulin bolus dose between 0.8 and 2 (I)U per 10 g CH (both inclusive). Expecting prandial insulin dose range for standardised meal test between 5 and 12 (I)U.
• BMI 18.5-28.0 kg/m^2 (both inclusive).
• HbA1c <= 9.0% by local laboratory analysis
• Fasting C-peptide <= 0.3 nmol/L.

Exclusion Criteria:

• Known or suspected hypersensitivity to trial products or related products.
• Type 2 diabetes mellitus.
• Previous participation in this trial. Participation is defined as randomised.
• Participation in any Clinical Trial within 3 months prior to this trial.
• Clinically significant abnormal haematology, biochemistry, lipids, or urinalysis screening tests, as judged by the Investigator considering the underlying disease.
• Presence of clinically significant acute gastrointestinal symptoms (e.g. nausea, vomiting, heartburn or diarrhoea), as judged by the Investigator.
• Known slowing of gastric emptying and or gastrointestinal surgery that in the opinion of the investigator might change gastrointestinal motility and food absorption.
• Unusual meal habits and special diet requirements or unwillingness to eat the food provided in the trial.
• Women of child bearing potential, not willing to use contraceptive methods.