Guided tissue regeneration (GTR) is a clinical procedure used to restore the attachment apparatus of periodontally diseased teeth. Guided bone regeneration (GBR) is a similar procedure used to augment bone of edentulous ridges. Both therapies enhance the ability of regenerative cells to repopulate wounds by using expanded polytetrafluoroethylene (ePTFE) membranes to exclude gingival fibroblasts and keratinocytes from the healing site. Cells were isolated from 12 membranes used in each procedure and screened for the ability to form mineralized nodules in vitro, a property of cells with osteogenic potential. Using zymography and reverse zymography, low-passage isolates of cells which formed nodules were examined for the expression of gelatinolytic and caseinolytic proteases as well as for proteinase inhibitors. These molecular data were then compared with clinical outcomes for each procedure. Cells isolated from regenerative membranes exhibited variable expression of 72 kDa gelatinase, fibroblast collagenase, stromelysin, tissue inhibitor of metalloproteinases (TIMP-1), and other unidentified proteases. The greatest proportion of clinical failures was associated with GTR therapy. Cells from GTR membranes which did not exhibit gains in clinical attachment often exhibited aberrant proteinase profiles. When compared with cells from GBR procedures, most cells from GTR procedures also secreted lower amounts of TIMP-1. The study shows that cells isolated from regenerative procedures produce degradative enzymes in vitro which may be related to the success or failure of the regenerative process in vivo. Generally, cells from unsuccessful GTR procedures produced low molecular weight gelatinases not associated with cells from successful cases.