The time interval between the study days is 2 to 28 days. At the clamp visits, subjects are connected to a Biostator (MTB Medizintechnik, Ulm, Germany) and receive an intravenous human insulin infusion (rate of 0.15 mU/kg/min) over the duration of each experiment to prevent a rise in endogenous insulin secretion. After a baseline period of 2 h the trial drug (6, 12, or 24 U of either Insulin Aspart or regular human insulin in random order) are administered s.c. with a syringe into the abdominal wall. Glucose infusion rates (GIR) necessary to keep blood glucose concentrations close to the clamp level of 90 mg/dl (5 mmol/l) are administered and recorded by the Biostator every minute for a period of 12 h post-dosing. Blood samples are drawn at regular intervals for the analysis of C-peptide and (depending on the trial drug administered) serum insulin or serum Insulin Aspart concentrations (measured with specific ELISAs).