At 08:00 hours in the morning at day 2, insulin infusion will be increased to 1.5 mU/kg/min for each subject and the Plasma Glucose will be kept at a plateau of 5.5 mmol/L by a controlled variable intravenous infusion of glucose (10% glucose enriched with 4mg [6,6-2H2] glucose /ml) for one hour. Afterwards, plasma glucose is allowed to fall to a plateau of 3.5 mmol/L, then to a nadir of 2.5 mmol/L, then to a blood glucose level of 4.0 mmol/L and finally back to a level of 5.5 mmol/L for safety reasons. Blood sampling for measurement of plasma glucose, [6,6-2H2] glucose (labelled glucose),glucagon, vital signs, hypoglycaemic symptoms questionnaire and hypoglycaemic awareness will be performed at each plasma glucose plateau. The subject will be discharged from the clinic at day 2, or later if deemed necessary by the investigator.