In RA patients, MMP-1 and MMP-3 in the serum, synovial tissue (ST) and fluid (SF), MMP-2 and MMP-7 in the SF, MMP-9 in the plasma and SF, MMP-12 and MMP-13 in the ST and SF have already been detected (Ahrens et al., 1996; Wernicke et al., 1996; Yoshihara et al., 2000; Moore et al., 2000; Tolboom et al., 2002; Green et al., 2003; Tchetverikov et al., 2003; Liu et al., 2004). Here, MMP13 is linked to rheumatoid arthritis.