solution form supplied form according to the manufacturer impranil elh solution in xylol isopropanol ethylglycol 29 20 21 ca 30 solution 40 parts of this solution were diluted with 5 parts isopropanol 40 parts toluol and 14 parts n n dimethylformamide the product used is identical to that of composition 2 a 30 solution of an aliphatic polyesterurethane produced by bayer ag leverkusen 200 parts of this solution were diluted with 25 parts acetone 150 parts toluol and 20 parts isopropanol the basic substance is a polyetherurethane in granulated form produced and sold by the upjohn company usa under the type designation 34 pellethane cpr 2363 u03bba urethane elastoplastic polymer 34 400 parts of this granulate were dissolved in 650 parts acetone 70 parts isopropanol and 300 parts n n dimethylformamide blood vessel prostheses produced according to the novel method of the invention may if desired be subsequently treated for example in order to make them hydrophilic or hydrophobic or negatively charged depending upon the desired boundary surface properties of the prosthesis the following treatments of the inner surface are preferably to be considered either singly or in suitable combinations these treatment methods are per se known in synthetic materials so that they need not.