Transplantation of cells secreting biologically active substances like cytokines, hormones or growth factors, may be a way of patient treatment in deficiency of these factors. Application of the permiselective barrier is the method of separation of the transplanted cells from the host cells to prevent the immune rejection. A review of polypropylene silanized hollow fiber membranes applications for immunoisolation of cells is presented. We have elaborated modified polypropylene membranes and applied them as the systems for isolation of cells. Modification of membranes by silanization allowed us to avoid tissue overgrowth during the implantation into mice. The applied membranes exhibited a stable cut-off value during about 3 months implantation into animal. The spectroscopic evaluation of absorption for red irradiation (FTIR) of the membrane material, revealed no differences in chemical structure before and after the implantation. The membranes were applied for isolation of hybridoma OKT3 cells secreting monoclonal antibody IgG2a reactive to human T lymphocytes, human parathyroid cells producing parathormon, WEHI-3B mouse cell line producing IL-3 (involved in the hematopoietic stem cells differentiation). Our separating systems were constructed with idea for immunoprotection of graft, for delivering of parathormon in hypoparathyroidism or for supporting of haematopoiesis. Summarizing, the elaborated membranes evaluated in the in vitro experiments and in the in vivo short animal experiments have turned out promising as systems for the local production of biologically active substances. (C) 2004 Elsevier B.V. All rights reserved.