Eighty-seven patients with moderate to severe acne were included in an 8-week randomized double-blind study to compare the efficacies of topically applied clindamycin phosphate 1% b.i.d., oral tetracyclines 500 mg b.i.d. and placebo. Patients were examined every 2 weeks and inflammatory lesions, i.e. papules and pustules were counted in the same area at each examination. Clindamycin phosphate demonstrated a highly significant 72% decrease of inflammatory lesions, as did tetracyclines with a 57% decrease, but not placebo (12%). Clindamycin phosphate was superior to tetracycline. No significant side effects were seen, in particular, no skin side effects.