This double-blind, parallel group study was conducted to evaluate the gastroduodenal safety and antiarthritic efficacy of a fixed combination of diclofenac sodium 50 mg and misoprostol 200 mcg, compared with a combination of diclofenac 50 mg and placebo. Three hundred and thirty-nine patients with rheumatoid arthritis and no significant gastric or duodenal mucosal damage were enrolled and received study medication (diclofenac/misoprostol, 164; diclofenac/placebo, 175) BID or TID for 12 weeks. Posttreatment gastroduodenal endoscopic examinations revealed ulcers in 11% of the diclofenac/placebo group, compared with only 4% of the diclofenac/misoprostol group (p = 0.034). Four-weekly assessments of arthritic condition revealed no clinically or statistically significant treatment differences. It was concluded that diclofenac/misoprostol caused significantly less gastroduodenal damage than diclofenac, but was as effective as diclofenac alone in the treatment of rheumatoid arthritis.