Thirty cases of clinical testing on the PVC drain tubes coated by a hydrophilic copolymer with long polyethylene oxide chains (PEO-COAT® drain tube) were carried out. As controls, non-coated PVC drain tubes were used. Thrombogenesis was observed in 24 out of 30 non-coated PVC drain tubes (80%) and only in 4 out of 30 PEO-COAT® drain tubes (13%). The PEO-COAT® drain tube significantly suppressed the absorption of plasma proteins and adhesion of platelets. The excellent antithrombogenic property of the hydrophilic polymer with long polyethylene oxide chains, which has been suggested by in vitro and in vivo experiments, was evidenced here clinically.