Systemic lupus erythematosus, a multisystemic disorder, is considered a prototype of the autoimmune diseases. Although its cause remains unknown, a viral etiology has been proposed. We report that a rapid and sensitive messenger RNA in situ hybridization technique detected hybridizing sequences to the human immunodeficiency virus type in the peripheral blood cells of a woman with systemic lupus erythematosus in whom the presence of acquired immuno-deficiency syndrome was reasonably excluded.