Interactions between a temperature-responsive poly(N-isopropylacrylamide)-grafted surface and blood platelets have been analyzed with computerized image analysis. Platelet behavior on this surface is dramatically dependent upon temperature in contrast to that on poly(ethylene glycol) (PEG)-grafted surfaces or polystyrene. The poly(N-isopropylacrylamide)-grafted surface interacts with platelets similarly as the poly(ethylene glycol)-rafted surface at 18 degrees C at 37 degrees C, platelets readily adhere onto the poly(N-isopropylacrylamide)-grafted surface similarly as to that of polystyrene.