The term "autoimmunity" has been used to categorize a number of different diseases of unknown etiology. The term as applied to many of these diseases would probably be interpreted best as "autoreactivity," as the clinical phenotypes are often characterized by an inflammatory-like accumulation of activated cells of the immune system at sites of obvious damage of normal cells and/or tissue. The reasons as to why an immune system should attack itself are far from clear, although the association with specific infectious diseases in genetically susceptible people remains perhaps our best lead. The input of the biotechnological revolution has enabled us to attempt to readdress many of the fundamental questions raised by clinical and serological associations with autoimmune disease. The ability to dissect the immune response to these infectious agents which are associated with autoimmune features (as well as the facility to identify new agents, e. g. HIV), in addition to the ability to clone and sequence immune response genes, has enabled a much better understanding, at least of the complexity of "autoimmunity" to be gleaned. This volume contains the chapters that summarize the plenary presentations given at The Impact of Biotechnology on AUTOIMMUNI1Y meeting in Florence, Italy in June 1993. They cover all aspects from pathogenesis to treatment. The association with infectious diseases and autoimmunity is comprehensively covered by David Isenberg who reviews major issues, such as the association of autoantibodies appearing after infectious disease and antibacterial antibodies associated with autoimmune disease.