Loss of connective tissue integrity occurs in many disease processes, including rheumatoid arthritis and osteoarthritis. Although there is a high incidence of these diseases in the developed world, there is no treatment that prevents the tissue damage that occurs. Several lines of evidence suggest that uncontrolled connective tissue metalloproteinase activity is responsible for the damage, and as a consequence the inhibition of these enzymes has become the target for therapeutic intervention. Several connective tissue metalloproteinases, including collagenase, stromelysin, and gelatinase, together with tissue inhibitors of metalloproteinases (TIMPs), have been described. Because of difficulties in isolating the metalloproteinases in sufficient quantity as pure separate enzymes, however, very little knowledge has accumulated about their detailed biochemistry. For similar reasons the way in which TIMPs inhibit tissue metalloproteinases is not yet fully understood. In this article it is shown how cloning metalloproteinase and TIMP cDNAs can provide information about the structure of these enzyme and inhibitor families and how the cDNAs can be used to generate recombinant cell lines from which enzymes and inhibitors can be readily purified for further studies.