A patient with oral pemphigus vulgaris and a patient with oral bullous pemphigoid were studied with immunofluorescence. The serum from both patients contained no demonstrable circulating antibodies, but direct staining of specimens obtained from the oral mucosa revealed characteristic fluorescence and established the diagnosis. The lack of circulating epidermal antibodies, therefore, does not rule out pemphigus and bullous pemphigoid. Direct immunofluorescence must be performed in order to exclude these diseases as a cause of chronic blistering of the oral cavity.