The efficacy and tolerance of proquazone, 900 mg, and ibuprofen, 1200 mg, were compared in a randomized, double-blind clinical trial of 6 months' duration, with 44 patients, 21 on proquazone and 23 on ibuprofen. Comparison of proquazone-treated patients with patients treated with iburofen showed a significantly better improvement , as is demonstrated by the significant differences in the Lansbury Index, in nocturnal pain, final assessment of therapeutic effect, and number of interruptions due to lack of efficacy. All differences were in favour of proquazone, proving its therapeutic superiority over ibuprofen. The side effects in the proquazone group were mainly gastrointestinal, and 2 patients broke off treatment prematurely due to diarrhoea (in one patient, lack of efficacy was a contributory cause). A third patient discontinued because of moderate nausea and dizziness. In the ibuprofen group, 4 patients discontinued because of side effects (skin eruptions, dizziness, epigastric discomfort, and one thrombocytopenia) in addition to lack of efficacy. Proquazone seems to be an effective and well tolerated anti-inflammatory analgesic.