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OBJECTIVE: To determine the possible role of the plasminogen activator (PA)/plasmin system in gouty arthritis. METHODS: We compared the antigenic values of urokinase-type PA (uPA), soluble uPA receptor (suPAR), and PA inhibitor type-1 (PAI-1) and the levels of matrix metalloproteinase-2 (MMP-2) and MMP-9 in 63 synovial fluid (SF) samples from knee joints of 38 patients with gouty arthritis and 20 SF samples from knee joints of 20 patients with osteoarthritis (OA). RESULTS: The increases of uPA, suPAR, and PAI-1 antigenic values in SF were associated with increased levels of latent MMP-9 (pro-MMP-9) (p < 0.001, p < 0.001, p < 0.001, respectively) in gouty arthritis, whereas a correlation was not observed between uPA, suPAR, and PAI-1 antigenic values and MMP-2 levels. Increased uPA, suPAR, and PAI-1 antigenic values in gouty arthritis SF were also correlated to each other (p < 0.001, p < 0.001, p < 0.001). In gouty arthritis SF, no significant relations were observed between uPA and suPAR antigenic values and leukocyte, neutrophil, or monocyte counts, while increased values of PAI-1 corresponded closely with increased leukocyte and neutrophil counts (p = 0.005, p = 0.004). Significantly higher values of the uPA, suPAR, and PAI-1 (p < 0.001, p < 0.001, p = 0.012) appeared in SF of gouty arthritis than in SF from patients with OA. CONCLUSION: These results show a correlation of the PA/plasmin system and MMP-9 in SF from patients with gouty arthritis, resulting in increased PA catalytic activity and contributing to inflammation in gouty arthritis.