A patient was presented who developed pure red cell aplasia while taking diphenylhydantoin (300mg/day) over a five-year period for the treatment of epilepsy. After discontinuation of diphenylhydantoin, the bone marrow showed a recovery from an erythroid aplasia and an intense reticulocytosis was observed in the peripheral blood. In spite of re-administration of diphenylhydantoin, anemia did not recur. The relationship between diphenylhydantoin and pure red cell aplasia was discussed.