Purpose: Human mesenchymal stem cells (hMSCs) hold the potential for bone regeneration because of their self-renewing and multipotent character. The goal of this study was to evaluate the influence of collagen membranes on the proliferation of hMSCs derived from bone marrow. A special focus was set on short-term eluates derived from collagen membranes, as volatile toxic materials washed out from these membranes may influence cell behavior during the short time course of oral surgery. Materials and Methods: The proliferation of hMSCs seeded directly on a collagen membrane (BioGide) was evaluated quantitatively using the cell proliferation reagent WST-1 (4-3-[4-iodophenyl]-2-[4-nitrophenyl]-2H-[5-tetrazolio]-1, 3--benzol-disulfonate) and qualitatively by scanning electron microscopy. Two standard biocompatibility tests, namely the lactate dehydrogenase and MTT (3-[4, 5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazoliumbromide) tests, were performed using hMSCs cultivated in eluates from membranes incubated for 10 minutes, 1 hour, or 24 hours in serum-free cell culture medium. The data were analyzed statistically. Results: Scanning electron microscopy showed large numbers of hMSCs with well-spread morphology on the collagen membranes after 7 days of culture. The WST test revealed significantly better proliferation of hMSCs on collagen membranes after 4 days of culture compared to cells cultured on a cover glass. Cytotoxicity levels were low, peaking in short-term eluates and decreasing with longer incubation times. Conclusion: Porcine collagen membranes showed good biocompatibility in vitro for hMSCs. If maximum cell proliferation rates are required, a prewash of membranes prior to application may be useful. Keywords: biocompatibility, collagen membrane, guided bone regeneration, human mesenchymal stem cells