Diflunisal (Fluniget, MK-647) was tested in an open clinical study with regard to its analgesic effect and its improvement of function in 30 patients suffering from osteoarthrosis of the hip and the knee. The treatment lasted for 4 weeks. The therapeutic effect was judged by the influence on day and night rest pain and on pain from pressure and movement, the change of morning stiffness and the functional improvement. Further judgement included general assessment by the physician and the patients. With Diflunisal the majority of the patients achieved a lasting improvement of their condition. A marked analgesic effect was observed during the first two weeks of therapy. Diflunisal was well tolerated. Laboratory data at the beginning and at the end of the four week treatment period revealed no toxic effects on organs, particularly no hematotoxic effects.