The levels of metalloproteases and inhibitor expression in synovial membranes were measured by analyzing mRNA of collagenase, stromelysin, and tissue inhibitor of metalloproteinase (TIMP-1) in this tissue from 20 healthy persons and 20 patients with osteoarthritis (OA). Our results indicated that while most of the normal synovia expressed TIMP-1 mRNA at low levels, very few expressed metalloproteinase mRNA. In contrast 40% of patients with OA expressed a moderate level of collagenase compared to 55 and 80% cases with considerably elevated stromelysin and TIMP-1 mRNA, respectively. The mRNA expression of collagenase (p < 0.032), stromelysin (p < 0.0001) and TIMP-1 (p < 0.008) was significantly higher in OA than in normals. The greater abundance of stromelysin mRNA relative to collagenase indicates differential regulation of the 2 genes. We also demonstrated an association of IL-1 with metalloproteinase gene expression.