Sixty hospital out-patients between 18 and 67 years of age entered this double-blind parallel study set up to compare ibuprofen 1200 mg daily with indomethacin 75 mg daily. Both groups of patients received one capsule three times daily. Ten patients withdrew from the trial because of side effects and a further 3 were excluded--one because of an incorrect diagnosis and 2 because of incomplete assessments--leaving the statistical analysis to be performed on 47 patients. Assessments made after one and two weeks showed significant improvement for the parameters of pain and tenderness at each examination in both treatment groups. Restriction of movement also showed improvement, though not reaching statistical significance. Although there was no statistically significant difference beteen the two drug groups the mean improvement in all three parameters was consistently better with ibuprofen than with indomethacin. The commonest side effects were related to the gastrointestinal tract. Altogether, 10 patients withdrew because of side effects--4 on ibuprofen and 6 on indomethacin. The gastric symptoms occurring with indomethacin appeared to be generally more severe and usually occurred early, within 3 or 4 days of commencing treatment, whereas patients on ibuprofen withdrew usually after 7 or 8 days.