The flow-sheet of <membrane bioreactor> for biotechnological application has been presented in the paper. The relevant topics that concern problems of microbial or <enzyme immobilization> as well as separation of reaction system onto the fractions with different residence time distributions have been overiewed. A set of conditions has been specified for membranes applied in the system. The following types of bioreactors have been characterized in detail i.e.:i) case of <enzymatic membrane> bioreactor for hydrolysis of penicillinum G and ii) case of microbial membrane bioreactor for culture and harvesting of biomass iii) microbial membrane bioreactor for alcohol fermentation.