Two cases of tuberculous arthritis with synovial fluid findings are presented, and the major series with culture results and synovial fluid analyses are reviewed. Synovial fluid cultures are positive for tuberculosis in almost 80 per cent of proved cases. Specimens obtained by open synovial biopsy are positive by histology or culture in over 90 per cent of proved cases. Little experience with closed needle biopsy has been published. About one-fifth of the patients with tuberculous arthritis will have a positive synovial fluid acid-fast smear for tubercle bacilli. The tuberculous synovial effusion invariably has an elevated protein level, fair to poor mucin clot formation and usually a low joint fluid sugar level. The synovial fluid white cell count is usually in the range of 10,000 to 20,000 cells/mm3, but it varies widely. Most fluids exhibited a predominance of polymorphonuclear leukocytes. The importance of bacteriologic or histologic study of the synovial fluid and membrane in establishing the diagnosis is emphasized. In general, this disease is different from tuberculous involvement of serous membranes both in the frequency of positive cultures and in the difference in cellular response.