Benoxaprofen (600 mg once daily) has been compared to indomethacin (25 mg 3 times daily) in a double-blind crossover study of 20 patients with active ankylosing spondylitis (AS). The clinical improvement was comparable with both drugs; 6 patients preferred benoxaprofen and 7 patients indomethacin. Although 2 patients discontinued benoxaprofen because of lack of effect, no upper gastrointestinal side effects were reported with this drug. Benoxaprofen is an alternative to indomethacin in the treatment of AS.