The clinical response of topical erythromycin (1%) in a new penetrative vehicle was evaluated in a double-blind investigation on 28 patients with severe and moderate acne vulgaris. The verum preparation was superior to the placebo in 21 of the patients, while in 4 the reverse was true and in 3 no differences were seen. It is thus obvious that topical erythromycin in the penetrative vehicle is a potent agent for acne treatment. The risk for development of resistant Propionibacterium acnes strains must, however, be considered in topical as well as in systemic antibiotic therapy of acne vulgaris.