During a prospective observation lasting 6 years 68 patients with rheumatic arthritis (RA) were repeatedly examined (up to 8 times) roentgenologically with parallel puncture biopsy of the synovial fluid of the knee joint made with an atraumatic needle, and numerical evaluation of markedness of 25 morphological signs of synovitis. A comparative analysis of the markedness of morphological signs of synovitis in relation to the degree and dynamics of destructive changes in the knee joint was made on the basis of the findings of 254 puncture biopsies and the same amount of roentgenograms. There is a close relationship between the activity of synovitis and the progress of destructive arthritis except for the morphological signs characterizing the reaction of hypersensitivity of an immediate type that may serve the purpose of prognostication of further articular destruction and of the choice of an early adequate therapy.