Forty patients with rosacea were treated topically with 0.75% metronidazole gel in a randomized split-face double-blind paired-comparison trial. With twice-daily applications, 36.7, 48.5, and 65.1 mean percent reductions in total papules and pustules were noted over baseline at 3, 6, and 9 weeks, respectively, on the side of the face receiving metronidazole therapy. Therapy with vehicle alone produced a maximum mean percent reduction of 14.9 at nine weeks. Erythema also responded but was less improved by the end of nine weeks of therapy. A mild increase in telangiectasia was noted on both actively treated and placebo-treated sides. The gel was locally well tolerated. Only two of 40 patients failed to complete the trial, both because of flares of rosacea (one at two days, and one at five weeks). No systemic symptoms were noted, and no consistent abnormalities were found in the results of laboratory studies (hematology, chemistry, and urinalysis). Topical metronidazole gel therapy appears to be a safe and efficacious therapy in the treatment of moderate to severe rosacea.