To the Editor.— Seborrheic dermatitis is a common skin disease of unknown origin. It erupts on the face, with erythema and scales and is somewhat disfiguring, leading to a seborrheic appearance, although the sebum excretion rate is normal. 1 Fungi are suspected agents, because treatment by oral and topical ketoconazole is effective, 2,3 but there are additional factors 4 and accompanying neurologic disorders are sometimes encountered as well. Since 1982, we have treated more than 30 patients with seborrheic dermatitis of the face with benzoyl peroxide at a concentration of 2.5% in a base (Panoxybase, Stieffel Laboratories). We recently reviewed the records of 30 patients, and report our results. The treatment was strikingly effective in all but two patients. Erythema and scales disappeared within a week. Irritant dermatitis was very mild in some patients (