The improved method of double-contrast arthrography for the knee joint, which can give extensive information on the intra-articular components, was undertaken in 131 knee joints with classical rheumatoid arthritis. Synovial proliferation was classified by its localisation into 6 types: nonproliferated (NP); localised, subdivided into suprapatellar pouch (SPP), proper articular (PA), and posterior (POST); panarticular (PAN); and burned out type (BO). These types are intimately related to the radiological stage and pathological changes of the articular cartilage and menisci. By following the dynamic changes of synovial proliferation by arthrography the clinical course of the rheumatoid knee joint may be predicted. While in the NP and SPP types destruction of the joint is minimal, it is relatively rapid and severe in the PA and PAN types. Thus the proliferation in the joint proper has a stronger influence on joint destruction than does the suprapatellar pouch. From these results synovectomy to resect proliferated synovial tissues of the joint proper completely, and to resect those of the suprapatellar pouch only superficially in the early stage, was undertaken in 21 rheumatoid arthritic joints, giving excellent results in 80.9%. The advantages of this method are discussed.