In rheumatoid arthritis (RA) joint inflammation is due to two processes: 1) the underlying inflammatory process (UIP) characterized by a lymphoplasmacellular infiltration of the synovial tissue, as well as pannus formation, and 2) the detritogenic synovitis (DS), a synovial response to articular wear products from cartilage and bone (detritus) that induces a preferentially fibrinous inflammation. In order to estimate the role of DS in the clinical presentation of such joints, 40 patients with RA undergoing knee-joint surgery on 48 occasions were evaluated for clinical parameters, radiological stage (Larsen), and histopathological characteristics of UIP and DS. The clinical parameters were comparable in knee joints with predominantly UIP or DS. However, DS was regularly seen in knees with advanced destruction according to Larsen's stages 4 to 5, while UIP occurres in joints even without radiological damage. In conclusion, it is assumed that the poor response of patients with advanced RA to so-called long-term drug therapy may be in part explained by the modifying influence of joint detritus on the underlying "rheumatoid" inflammatory process.