24 patients suffering from papulo-pustular acne were treated with mono-therapy with 2% erythromycin-containing alcoholic solution for eight weeks. Pustular lesions responded promptly, followed by inflammatory papules. Microbiological investigations revealed a lack of propionibacteria as well as reduction of pathogenic staphylococci. Patients after extended local erythromycin treatment did not show any erythromycin serum levels.