Nonsteroidal anti-inflammatory drug (NSAID) gastropathy is now a commonly recognized and reported complication of such arthritis therapy. Significant gastric lesions develop in up to 40 percent of arthritic patients treated with long-term anti-inflammatory doses of NSAIDs, 20 percent of which represents actual ulcer crater disease. This 12-week endoscopy-controlled, double-blind study was constructed to evaluate the safety and efficacy of nabumetone 1,000 mg at bedtime compared with naproxen 250 mg twice daily. A total of 37 patients completed the study, including 29 patients with a diagnosis of osteoarthritis and eight with a diagnosis of rheumatoid arthritis. By posttreatment endoscopy, nabumetone was significantly less toxic to the gastrointestinal tract than was naproxen. The nabumetone-treated group also showed greater improvement in all efficacy variables, with significant improvement noted in three of these five variables in both rheumatoid and osteoarthritic patients.