The DPT-1 is a multicenter, randomized, controlled, NIH-sponsored clinical trial to assess whether low dose subcutaneous insulin (compared to a non-intervention control group) or oral insulin (compared to placebo) prevents or delays the onset of type I diabetes mellitus (IDDM) in relatives of IDDM subjects at risk. Screening consists of islet cell antibodies (ICA); staging (in those positive with positive ICA) includes intravenous glucose tolerance testing, insulin autoantibodies, and HLA typing.