In a parallel, double-blind and randomized trial of 6-weeks' duration, flurbiprofen (150 mg to 200 mg daily) was compared with indomethacin (75 mg to 100 mg daily) in the management of 26 patients with active ankylosing spondylitis. None of the patients in either group withdrew from the study because of lack of efficacy of the drugs. Both drugs were equally effective in the relief of pain and tenderness of the affected joints. Overall subjective improvement, assessed by the patient and the investigator at the end of the trial, was present in 90% of the patients in the flurbiprofen group and in 75% of those in the indomethacin group. The mean values of all the spinal motion tests improved in the flurbiprofen group but not in the indomethacin group. Statistically significant improvement in the Schober test was achieved in the flurbiprofen group and in chest expansion in the indomethacin group. Characteristic untoward effects related to the central nervous system and gastro-intestinal tract were present in a few patients in both groups.