Rheumatoid hyperplastic synovial lining cells and sublining fibroblasts are known to produce, in vivo and in vitro, matrix metallo-proteinases which degrade extracellular matrix components of joints. We have studied by immunohistochemistry and in situ hybridization the presence of matrix metallo-proteinase stromelysin 3 and its potential inhibitors TIMP-1 and TIMP-2 in 5 cases of normal synovia, 5 cases of chronic synovitis and 12 cases of rheumatoid arthritis. Few hyperplastic synoviocytes and some sparse fibroblasts have been found to produce stromelysin 3 in all rheumatoid arthritis and 2 chronic synovitis. Stromelysin 3 seems to have a limited role in the destructive process of extracellular matrix. TIMP-1 and TIMP-2 were largely expressed principally in hyperplastic synoviocytes and in endothelial cells of all rheumatoid synovitis and 2 chronic synovitis. These findings plead for a balance between matrix metallo-proteinases and their inhibitors in these inflammatory lesions.