Adverse experiences were monitored in 1,681 patients with rheumatoid arthritis (RA) or osteoarthritis to evaluate the safety of benoxaprofen at daily doses up to 1,000 mg during long-term therapy. Gastrointestinal side effects with benoxaprofen compared favorably to those reported during aspirin and ibuprofen therapy, with peptic ulcers reported in 0.4% of the patients or 1 ulcer for 200 patient years. The incidence of photosensitivity or onycholysis was 9%. Laboratory examinations revealed no significant changes in BUN, hematocrit, hemoglobin, SGOT, and SGPT values. The only trend toward abnormal values was seen in the LDH in patients with RA.