integrating the properties of synthetic membranes with biological catalysts such as cells and enzymes forms the basis of an exciting new technology called membrane bioreactors. the impetus behind this marriage comes from the recent spectacular advances in recombinant dna and cell fusion technologies and the need to develop competitive bioprocessing schemes to produce complex and active biological molecules. the advantages and limitations of using membrane bioreactors for entrapping whole cells and enzymes are reviewed. various membrane configurations such as microcapsules, hollow fibers, and flat sheets are compared. several different entrapped membrane bioreactors, including single, laminated and microporous, for the conversion of optically active enantiomers are described. as with new and exciting technologies, the future of membrane bioreactors in biotechnology will depend on their ability to produce desired molecules at competitive costs. (author abstract) 85 refs