Flurbiprofen (Ansaid, Upjohn), a potent new analgesic and anti-inflammatory agent, was compared with phenylbutazone in 90 patients with ankylosing spondylitis. In this double-blind, randomized, 26-week study, a total daily dose of 200 mg of flurbiprofen, administered three times daily, was as effective as 300 mg of phenylbutazone in controlling the pain and other symptoms of ankylosing spondylitis. In some patients, symptoms were adequately controlled by 150 mg of flurbiprofen per day, administered twice daily. There were no statistically significant differences between flurbiprofen and phenylbutazone in the investigators' and patients' assessments of improvement at all key follow-up periods. In addition, there were no consistently significant differences between drugs in the efficacy pain scales and quantitative measurements studied. Flurbiprofen was well tolerated in doses of up to 300 mg per day, and no clinically significant laboratory abnormalities were detected. Flurbiprofen appears to be an excellent alternative to phenylbutazone in the management of patients with ankylosing spondylitis.