At each menstrual cycle, the uterine endometrium undergoes intense remodelling. Of the many factors implicated in tissue remodelling, the matrix metalloproteinases (MMPs) play a central role owing to their capacity to degrade the extracellular matrix. The aim of this study was to examine the nature and cellular origin of endometrial proteases as evaluated in culture systems with clearly characterized cell types. Endometrial cells from hysterectomy specimens were prepared using collagenase digestion. Bone-marrow-derived cells (a known source of proteases) were removed by immunopurification. Cells were cultured on different substrates (matrigel, agarose, glass or plastic). Purity of cell preparations was examined by immunocytochemistry, and proteases were characterized by zymography on SDS-PAGE containing gelatin. The cell phenotype in culture was largely influenced by the type of substrate. Gelatin-degrading enzymes detected in culture supernatants of stromal and epithelial cells had molecular masses ranging from 42 to 248 kDa, and were identified as metalloproteinases. We conclude that human endometrial stromal and epithelial cells express several matrix metalloproteinases, the expression of which clearly depended on the purity of cell preparation, on cell adhesion and on the nature of the substrate on which the cells grew. These enzymes might be involved in endometrium remodelling, blastocyst implantation and trophoblast invasion.