Abstract: Plastic resinous tubes, particularly for medical use is improved in blood compatibility when brought into contact with blood, by applying a low-temperature plasma treatment to inner surfaces of the tubes, which plasma is produced through electrodeless electric discharges by the effect of microwave to make it possible to prevent the tube from being heated in such a treatment. The inner surfaces of the tubes thus activated may be further subjected to an inner surface graft copolymerization treatment to enhance blood compatibility.

Abstract: A highly blood-compatible material comprising a polymeric base material and water-soluble and substantially nonionic polymer(s) directly attached to the surface of the base material in an amount of 1 to 100 .mu.g/cm.sup.2. The polymeric base material is preferably in the form of a web and composed of polyurethane, ethylene/vinyl acetate copolymer or polyvinylchloride. In addition, the attached polymers may be selected from the group consisting of acrylamide polymers, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, and dextran. This material is particularly useful for preparing vascular prosthesis of small diameters.