Two human disease, kuru and Creutzfeldt-Jakob disease, and two animal diseases, scrapie and mink encephalopathy, comprise the group designated the subacute spongiform encephalopathies. Studies on these four classic conditions have generated a new philosophy, new concepts, and new technology that provide a basis for the study of chronic diseases and latent infections of man and animals. These aspects are discussed more broadly and in variable detail in the references listed on the following page.