In a multiclinic double-blind trial, 253 patients with moderate to severe acne vulgaris were treated with erythromycin, 1.5% topical solution (n = 127), or the vehicle (n = 126). The preparations were applied twice daily for 12 weeks. The response to treatment was evaluated by lesion counts and overall clinical judgment at 2, 4, 8, 10, and 12 weeks after initiation of treatment. The reduction in the number of inflammatory lesions, papules, and pustules was significantly greater (p < 0.01) in the erythromycin-treated group. The global evaluation of the clinical response correlated well with the reduction in the lesion counts. No serious adverse effects were encountered.