Types I to VI collagens were immunolocalized in normal and rheumatoid synovium using monospecific antibodies. Immunofluorescence studies showed type VI in the extracellular matrix of the lining cell layer, whereas positive staining for type III collagen was observed in both the lining and sublining cell layers. All other collagens could not be detected in the lining cell layer. Immunogold staining of the rheumatoid synovium localized type VI collagen to filamentous material, which was the major extracellular structure of the lining cell layer. Type III collagen was associated with thin cross-striated collagen fibrils. A brief treatment of rheumatoid synovial tissue with bacterial collagenase produced in the lining cell layer numerous broad-banded fibrils with 100-nm periodicity; these fibrils could be labeled with the antibody against type VI collagen. This suggests that type VI collagen filaments have the potential to form periodic structures under certain conditions. We further studied the susceptibility of type I to VI collagens to matrix metalloproteinase 1, 2 and 3 (collagenase, gelatinase of molecular weight 72,000, stromelysin), which are secreted by synovial lining cells in rheumatoid synovium, and found only type VI collagen to be completely resistant to all these metalloproteinases. These data indicate that type VI collagen, which has the ability to bind to cells and to interstitial collagens, plays an important role in supporting the synovial lining cells in the normal and rheumatoid synovium.