Insulin-dependent (type 1) diabetes is a frequent disease with an incidence of up to about 1%. It requires daily treatment and serious late complications are observed. Good animal models exist for studying diabetes. These can be categorized as animals with spontaneously developing diabetes (BB rats, NOD mice) and as animals with induced diabetes (e.g. by virus). Immunodeficient nude mice have also been widely used. None of the models is perfect, but each has contributed to our present knowledge of the disease. Studies on the pathogenesis of type 1 diabetes are given as an example. Recently, experience with prophylactic treatment of animals in order to prevent diabetes has been applied to humans with promising results.