The adhesion and growth of two pathogenic bacteria (Escherichia coli and Staphylococcus aureus) on the surface of a heparinized hydrophilic polymer were studied. Heparinized hydrophilic polymer is composed of poly(vinyl chloride) grafted with poly(ethylene glycol) monomethacrylate, diethylaminoethyl methacrylate, and ionically bound heparin. Poly(vinyl chloride) was used as a control. Plasma protein pre coated polymers were also prepared to evaluate the effect of proteins on bacterial adhesion. Polymer films were stored in bacterial suspensions under gentle shaking at 37 degrees C for 24 hr. The amount of adherent bacterial cells was measured by the bioluminescent assay of bacterial adenosine triphosphate. Their structure was observed by use of a scanning electron microscope. These evaluations demonstrated that a large amount of bacterial adhesion and biofilm formation was found on the surface of poly(vinyl chloride), whereas significant reductions in bacterial adhesion and no biofilm formation were observed on heparinized hydrophilic polymer. Bacterial adhesion onto plasma protein pre coat polymer films were also investigated, and it was clear that the bacterial adhesion on these surfaces was dependent upon the amount and species of absorbed proteins.