Abstract: Synthetic material apt to stably adsorb high quantities of heparin, consisting of a polyurethane resin, cross-linked with copolymeric chains in correspondence of at least part of its own urethane groups ##STR1## as per the following general formula: ##STR2## wherein, PU--- is a polyurethanic polymeric chain,R.sup.1 is an alkyl or aralkyl, containing functional groups inert to isocyanates,R.sup.2 is an alkylene,R.sup.3 is an alkylene, arylene or other bivalent organic radical, andR.sup.n is a polyamidoaminic radical;and process for the production of said material.