The purpose of this study was to investigate synovial levels of matrix metalloproteinase-1 (MMP-1), known to break down collagen, and tissue inhibitor of metalloproteinase (TIMP-1), its natural antagonist, in patients with various inflammatory disorders. Eighty-five patients with different inflammatory arthritides (20 Behcet's disease, 20 familial Mediterranean fever, 26 rheumatoid arthritis and 19 osteoarthritis) were enrolled in the study. Synovial MMP-1 and TIMP-1 levels were measured by two-step sandwich ELISA. There were significant differences between study and control groups regarding erythrocyte sedimentation rate, C-reactive protein, MMP-1 and TIMP-1 values, The synovial MMP-1 levels. of patients with Behcet's disease and familial Mediterranean fever were no different from those in patients with rheumatoid arthritis, but significantly higher than those of patients with osteoarthritis. The synovial TIMP-1 levels in patients with osteoarthritis were higher than those of patients with the other three diseases, among which the difference was not statistically significant, and the difference between osteoarthritis and the others was statistically significant. Because of the detection of similar levels of synovial MMP-1 in patients with familial Mediterranean fever, Behcet's disease and rheumatoid arthritis, we conclude that the absence of erosions in patients with familial Mediterranean fever and Behcet's disease may be explained by MMP-1 being a marker of cytokine-driven inflammation, or by the short-lived and transient nature of the arthritis observed in these patients.