One hundred three patients with acne vulgaris were randomly designated to receive either a topical formulation of erythromycin plus zinc or a topical solution of 1 % clindamycin phosphate (Cleocin-T). The patients treated themselves twice daily and were examined at 3, 6, 9, and 12 weeks after the start of therapy. By week 6 the overall severity grade was consistently lower and the percent reduction of severity, papules, pustules, and total comedones was higher in the erythromycin-zinc-treated group than in the clindamycin-treated group. In the 92 patients who completed this study (48 receiving erythromycin-zinc and 44 receiving clindamycin), no serious topical or systemic side effects were reported. Two patients, one from each treatment group, suffered mild irritation. One patient was withdrawn from the erythromycin-zinc-treated group. Results of patch tests were negative. The superiority of the erythromycin-zinc formulation may be due to the increased (4%) erythromycin concentration and/or the ability of 1.2% zinc acetate to enhance the product's activity.