This crossover, glucose-clamp study will investigate the impact of different basal insulin infusion rates on glucose control employing insulin pumps with different insulin delivery regimen. Patients will be randomized in one of 2 groups, to receive on the first study day insulin via pumps with pulsatile or quasi-continuous delivery modes. On the second study day they will be switched to treatment with the alternative delivery regimen. The anticipated duration of the trial is 2 study days and the target sample size is 14 individuals.

Inclusion Criteria:

• Male patients 18-65 years of age
• Type I diabetes mellitus
• Currently on continuous subcutaneous insulin infusion therapy

Exclusion Criteria:

• Proliferative retinopathy or maculopathy requiring actue treatment within last 6 months
• Use of systemic corticoids in last 3 months
• Treatment with medication known to interfere with glucose metabolism