The effect of corticosteroid (or ACTH) therapy on 4 patients with idiopathic granulomatous hepatitis is described. All patients presented with spiking fever and chills and none had jaundice. Only 1 patient had an enlarged tender liver and 3 had splenomegaly. The erythrocyte sedimentation rate was increased in all cases while the white blood cell count was typically normal. Impairment in liver function was insignificant and consisted of a mild elevation of SGOT and alkaline phosphatase activities and prolonged prothrombin time. All patients presented a diagnostic challenge. The diagnosis was established by routine liver biopsies in 3 cases and by laparotomy in the 4th. The etiology could not be established. All patients reacted dramatically to prednisone (or ACTH) after failure of other therapeutic regimens. The disease has, however, been present for 5 years in 1 patient and 10 years in another. Relapses occur after cessation of therapy.