Vascular grafts made of expanded polytetrafluoroethylene (ePTFE) are widely employed in reconstructive surgery. Despite their successful use for replacement of large diameter blood vessels, ePTFE vascular grafts with internal diameters of less than 6 mm uniformly fail as a result of blood clot formation. To reduce the ePTFE reactivity to platelets, a new method for membrane construction on the inner graft surface was developed. The membrane, made of a chitosan-poly(vinyl alcohol) blend and non-ionic detergent, is constructed by adsorption of a thin liquid film and air drying. The chemically modified ePTFE surface exhibits both morphological changes and a markedly reduced reactivity to platelets in in vitro studies. Chemical activation of the chitosan-poly(vinyl alcohol) blend, to trigger desired protein binding, may yet serve as a complementary surface modification approach.