This volume in the series Developments in Medical Virology deals with viruses involved in diabetes mellitus, a syndrome with a strong genetic background that causes damage to the regulation of insulin synthesis and function. Viruses were found either to cause or to stimulate diabetes mellitus in man and in animal models. The nature of the role of viruses is described by many of the scientists who participated in the original studies. To complete the picture, chapters were included that deal with the insulin gene, the secondary structure of the proinsulin and insulin receptor polypeptides, pancreatic Langerhans islets, and clinical considerations of the disease. The aim of Developments in Medical Virology is to elucidate processes involving viruses as pathogens of cells and organisms, with special attention to human diseases. A number of volumes will be devoted to viruses affecting specific organs (e.g. brain, liver, etc.), while others will elaborate on the clinical experience in the use of antiviral drugs. The series is published in parallel with Developments in Molecular Virology, designed to present an analysis of molecular mechanisms implicated in virus infection and replicative processes. In addition, the series Developments in Veterinary Virology provides information on viruses causing diseases in animals, with special emphasis on aspects of interest to veterinarians.