In two patients who had been receiving prolonged anticonvulsant drug therapy for epilepsy there appeared a syndrome indistinguishable from systemic lupus erythematosus (SLE). One, an 8-year-old boy who had been treated since the age of 3, died as a result of severe hemorrhagic manifestations. The other, a woman 19 years of age, had a similar history, and tests with LE cell preparations performed with peripheral blood were positive on 3 consecutive daily examinations; the test became negative and her musculoskeletal complaints disappeared when the treatment with trimethadione was discontinued. The authors suggest that some drugs may have the effect of unmasking a latent form of SLE.