The objective of this study has been the well established fact that proinflammatory cytokines and metalloproteinases play a crucial role in the pathogenesis of chronic arthritis as well as the development of pannus, with the eventual erosive changes. Among the proinflammatory cytokines, interleukin-18 (IL-18) has been shown to contribute to the pathogenesis of chronic synovitis by increasing the secretion of interleukin-1beta (IL-1β) and the tumor necrosis factor-alpha (TNF-α) and also stimulating angiogenesis. The aim of this study is to investigate the synovial IL-18, IL-1β, TNF-α and matrix metalloproteinase-3 (MMP-3) levels in patients with Behçet’s disease (BD), and compare them with the levels of patients with rheumatoid arthritis (RA) and osteoarthritis (OA). 30 patients with BD, 20 with RA, and 20 with OA were included in the study. The synovial levels of IL-18, IL-1β, TNF-α and MMP-3 were detected using the two-step sandwich ELISA method. The synovial IL-18, TNF-α and MMP-3 levels were significantly higher in RA patients than patients with BD (P=0.004, 0.019, 0.025, respectively) and with OA (P=0.004, 0.045, 0.032, respectively). There were no differences, with respect to the cytokine levels, when patients with BD were compared with those with OA. Patients with RA and BD had higher IL-1β levels than patients with OA (P=0.017, 0.013, respectively). However, no such difference was found for IL-1β between BD and RA patients. Among patients with RA, positive correlations were found between TNF-α and MMP-3 (r=0.683, P=0.001). Our results showed that MMP-3 and proinflammatory cytokines, except IL-1β, were expressed in relatively small quantities in Behçet’s synovitis. Detection of the lower levels of these cytokines and metalloproteinases might explain the non-erosive character of Behçet’s arthritis. We suggest that IL-1β may be involved in the pathogenesis of Behçet’s synovitis.