Forty patients with definite or classical rheumatoid arthritis were entered for 3 months in a double-blind trial, 20 patients on 400 mg fentiazac or 200 mg sulindac daily. Statistically significant improvements on fentiazac were reported during the course of the study for 3 of 7 parameters: pain score, total joint score and number of swollen joints, while for sulindac a significant improvement was reported for 6 parameters: pain score, grip strength, joint size, total joint score, number of swollen joints and erythrocyte sedimentation rate. Side-effects were reported during the 3-month comparative period for 3 patients receiving fentiazac, consisting of rash, headache, epigastric pain, and for 1 patient receiving sulindac who suffered from gastro-intestinal intolerance. Because of ineffectiveness and/or side-effects, the treatment had to be discontinued for 5 patients in the fentiazac group and for 3 in the sulindac treatment group. The results support earlier evidence that fentiazac and sulindac have analgesic and anti-inflammatory properties controlling disease activity in rheumatoid arthritis, sulindac being the more effective. During a long-term tolerance study, 3 of 33 patients continued on fentiazac developed a reversible hepatotoxicity possibly due to the drug.