Although the precise events preceding insulin-dependent diabetes mellitus (IDDM, type 1 diabetes) have not yet been elucidated, it is known that IDDM results from a slow, progressive, immune process directed against pancreatic islet beta cells. Disrupting this autoimmune process has been the focus of research aimed at preventing or slowing the disease progression. Technologic advances in predicting the onset and likelihood of developing IDDM have made it possible to study the effects of early immune intervention. The National Institutes of Health recently launched a large-scale, multicenter trial to evaluate the effectiveness of insulin as preventive therapy. Although many different immunosuppressive and immunomodulating agents have been investigated, the use of insulin as a prophylactic agent is a fairly recent concept. Several methods have been used to halt the autoimmune destruction of the pancreas, with animal and human studies serving as the basis for insulin in preventing IDDM.