The Diabetes Prevention Trial of Type 1 (DPT-1) is a multicenter randomized, controlled clinical trial designed to determine whether it is possible to delay or prevent the clinical onset of type 1 diabetes through daily doses of insulin in individuals determined to be at risk for the disease. The parenteral insulin trial in DPT-1 has been completed, however, the oral insulin trial is still recruiting. Over 350 sites in the United States, Canada, and Puerto Rico are taking part in the study. Screening of patients is ongoing; approximately 100,000 nondiabetic relatives of persons with type 1 diabetes have been screened to detect the presence of islet cell antibodies. Those individuals found to have islet cell antibodies are being staged to determine their risk of diabetes based on genetic, immunologic, and metabolic characteristics. Those individuals found to be at intermediate risk of diabetes are randomized to receive insulin orally or to receive placebo. Patients are being followed for up to six years.