The objective was to investigate the presence of Mycoplasma and Chlamydia in the synovial fluid of patients with rheumatoid arthritis (RA) and other chronic arthritides. Samples of synovial fluid (SF) were collected from all patients presenting with an articular effusion. Seventy SF samples were subjected to study for Mycoplasma and cultured on standard media for Mycoplasma. The 70 other SF samples were subjected to study for the presence of Chlamydia and cultivated on cell cultures specially MC coy cell lines. All standard cultures for Mycoplasma and Chlamydia remained negative, consistent with the fact that synovial fluid is sterile, despite of many investigations that have indicated DNA of some bacteria in the SF of patients with arthritis. However, as many other attempts to detect the presence of these fastidious organisms in the joints of patients with such arthritides have failed, the question of their possible roll in the pathogenesis of human rheumatic diseases remains controversial and needs to be re-examined.