We report a case of refractory erythema multiforme associated with atypical epidermal autoantibodies. The patient was a 63-year-old woman with clinical and histologic features of erythema multiforme and a large mediastinal T cell lymphoma. Immunofluorescence studies disclosed high serum titers of cell surface antibodies against epidermal keratinocytes in a pattern typical of pemphigus vulgaris. The epidermal antigen reacting with these circulating antibodies was characterized by incubating ¹⁴C-labeled keratinocytes with serum. The patient's serum pattern precipitated multiple proteins (keratinocyte antigens), but not the 130,000- and 85,000-dalton polypeptides characteristic of pemphigus vulgaris. Thus autoantibodies reacting selectively with non-pemphigus vulgaris epidermal keratinocyte antigens may be the cause of a false-positive immunofluorescence test for pemphigus vulgaris.