Epidermolysis bullosa acquisita (EBA) is an autoimmune-mediated subepidermal bullous disease in which the target of the autoantibodies is type VII collagen, a major component of anchoring fibrils. The purpose of this study was to evaluate the complement-fixing abilities and IgG subclass distribution of autoantibodies in EBA, and to also attempt to investigate the relation between inflammation, complement fixation and IgG subclass distribution in EBA patients. Only 2 sera of 18 patients (11%) showed weak complement-fixing abilities. IgG1 and IgG4 were the most frequently and intensely stained IgG subclasses in EBA sera. We could not find any relationship between the clinico-pathologic types, complement-fixing abilities and IgG subclasses in EBA. These results suggested that complement activation may not be a key factor of bulla formation in EBA.