The tolerance and effectiveness of Ibuproxam were investigated in 54 patients with arthrosis, R.A., ankylosing spondylitis, and fibrositis. Statistically significant reduction of pain at the end of the treatment was accompanied by decreased limitation of joint movement and morning stiffness. Simultaneous investigation of clinical and biological tolerance showed that the drug is infrequently responsible for side-effects that are always of negligible importance. Oesophagogastroduodenoscopy in subjects with a prior history and/or signs of active pathology of the upper digestive tract did not reveal exacerbation or recrudescence of lesions, nor the appearance of acute lesions.