Normal human skin fibroblasts in monolayer cultures have been shown to produce both procollagenase and a specific inhibitor of the active form of this enzyme. Investigations into the kinetics of action of fibroblast collagenase are planned, in particular with regards to substrate specificity, activation energy, deuterium isotope effects, and enzyme-substrate binding. Fibroblast inhibitor has been purified from serum-containing culture medium and we are attempting to obtain a functionally monospecific antiserum. Such an antiserum will permit the development of an ELISA assay and will also allow for the initiation of studies designed to investigate inhibitor biosynthesis and tissue localization. Disease states such as morphea, scleroderma, connective tissue nevi, epidermolysis bullosa, and rheumatoid arthritis are all characterized by histological abnormalities in collagen. Since fibroblast inhibitor likely represents the major control mechanism of collagenase activity following extracellular activation of this enzyme, the role of this inhibitor in normal connective tissue turnover and in the above disease states will also be investigated.