Adsorption of proteins (fibrinogen, albumin, and gamma globulin) from plasma onto surface-modified PUS (PU-PEO, PU-SO,, and PU-PEO-SO,) was evaluated. Adsorbed fibrinogen at steady state decreased in the order PU-SO, > PU > PU-PEO-SO, > PU-PEO, suggesting that sulfonate groups have specific high affinity to fibrinogen. The intermediate fibrinogen adsorption on PU-PEO-SO, can be explained by the compensatory effect between the low protein binding affinity of the PEO chain and the high fibrinogen binding affinity of the sulfonate group. In addition, PU-PEO-SO, showed a very fast fibrinogen adsorption due to the high accessibility of the sulfonate group to fibrinogen by the poly(ethy1ene oxide) (PEO) spacer. The kinetic pro-files of their surfaces showed that as the adsorption time increases, fibrinogen initially adsorbed was decreased and a plateau reached, demonstrating that all the surfaces exhibited the Vroman effect (the fibrinogen displacement phenomenon). PU-PEO showed the least fibrinogen and albumin adsorption among PUS, confirming the known nonadhesive property of PEO chains. It is very interesting that PU-PEO-SO, exhibited the highest adsorption of albumin and the lowest adsorption of IgG. Therefore, it may be concluded that such adsorption behaviors of proteins to PU-PEO-SO, contribute to improved blood compatibility.