Prevention of Diabetes Progression Trial (PDPT)

Inclusion Criteria: * Newly diagnosed type 1 diabetes without previous insulin or oral hypoglycemic therapy. * ages 2 to 40 years at diagnosis * enroll within 3 months of diagnosis * test positive for at least one of the biochemical autoantibodies (ICA-512, GAD 65 or IAA) prior to enrolling Exclusion Criteria: * Previous treatment with an anti-IL-2 directed monoclonal antibody or any other investigational agent that would interfere with the ability to evaluate the safety and efficacy of daclizumab. * Other immunosuppressive drugs including, but not limited to, corticosteroids, cyclosporine, tacrolimus, rapamycin, mycophenolate mofetil, or azathioprine. * Active significant infection * Limited life expectancy because of disease other than diabetes * Pregnancy