Two patients with established systemic lupus erythematosus developed bullous dermatoses clinically suggestive of bullous pemphigoid (BP). Direct immunofluorescence demonstrated linear staining at the dermoepidermal junction for IgG and C3 in a pattern typical for BP. However, immunoelectron microscopy demonstrated deposits of IgG largely below the basal lamina, with little if any deposit present within the lamina lucida. These findings are consistent with systemic lupus erythematosus (SLE) and effectively rule out BP. In addition, the leukocyte attachment assay, an in vitro assay of the functional activity of tissue-deposited immune complexes, demonstrated strong attachment of leukocytes to the dermoepidermal junction of patients' skin, suggesting that the immune reactants were functional immune complexes of possible importance to the pathogenesis of the bullous lesions. To our knowledge, this is the first time that immunoelectron microscopy has been performed on skin from patients suspected of manifesting concurrent SLE and BP. Our findings cast doubt on previous such reports by demonstrating the existence of a bullous form of SLE resembling BP both clinically and by direct immunofluorescence. (J AM ACAD DERMATOL 7:511-520, 1982.)