The recognition of antibodies by the immune system is more complex than previously believed. Rheumatoid factor (RF), a family of autoantibodies against gammaglobulin, has long been recognized as an important biologic marker for rheumatoid arthritis (RA). When RF contributes to the generation of the inflammatory aspects of RA, it probably does so by forming immune complexes that are themselves able to bring about the inflammatory response. Contrary to the widely accepted belief that RF somehow is triggered by recognition of self IgG, antibodies to viral Fc receptors may provide the initial stimulus for RF production in RA.