A hereditary basis for the predisposition to several autoimmune diseases has long been suspected. A relationship between diseases and genes that encode various immune effector proteins is now recognized. Many of these genes are components of the major histocompatibility complex (MHC). Recent studies have provided insights into the mechanism by which MHC antigens can influence the tendency to the expression of autoimmune disease. These findings have also provided the rationale for designing specific immunotherapeutic interventions. © 1992.