Abstract: The present invention provides a method for synthesis polypeptides in a cell-free system by which products of synthesis are branched in a low molecular weight fraction and a fraction which contains high molecular weight components with the target polypeptide, the main part of the low molecular weight fraction is removed via at least one part of the second porous barrier, the ratio of the volume of the fractions of feed solution and expendable components to the volume of the fraction containing the target polypeptide is chosen, modes of supply of the feed solution and expendable components of the fraction are realized.