We examined the effects of an inhibitor of 5-lipoxygenase (A-64077) in 11 patients with mild to moderately active ulcerative colitis (UC). Treatment was a daily oral dose of 800 mg for 28 days. Physicians global rating (scale 1-50) included stool characteristics, rectal bleeding, abdominal and rectal pain, urgency, and general well being; sigmoidoscopic evaluation (scale 1-15) included mucosal vascular pattern, erythema, granularity/ulcerations, friability, and exudate. All of the patients experienced a decrease in discomfort of their disease, and the gross appearance in the sigmoidoscopy improved in eight of them, but were not accompanied by histologic improvement. No significant side effects occurred. A long-term controlled double-blind and dose-effect trial using 5-lipoxygenase inhibitors is needed which may lead to a new therapeutic approach in UC.