Type 1 diabetes of both the NOD mouse and man is associated with autoimmunity directed against insulin which is the only beta cell specific autoantigen identified to date. One can use autoantibodies to insulin to predict diabetes, use insulin peptides to create insulin autoantibodies, insulitis and diabetes, and use insulin or its peptides in animal models to prevent diabetes. An expanding set of resources are now available for the development and testing in man of therapies to prevent type 1 diabetes, and a number of trials utilizing insulin peptides are now underway.