Forty-two patients with ankylosing spondylitis were entered into a double-blind study to compare treatment with indomethacin and a new non-steroidal anti-inflammatory drug, nabumetone. Clinical, laboratory and side-effect profiles were measured over a three month period. Both drugs were effective in relieving pain and morning stiffness, indomethacin was better in alleviating general stiffness, nabumetone resulted in less side-effects. Objective measurements of spinal movements revealed no difference between the two drugs. Nabumetone, available as Relifex, appears as effective as indomethacin in relieving the symptoms of ankylosing spondylitis and is possibly better tolerated.