A new technique for the prevention of platelet adhesion on the polysulfone (PSf) porous catheter system by means of saline perfusion was investigated. Commercially available ultrafiltration PSf hollow fibers were used as porous catheter tubes. Sixty milliliter of citrated canine blood was circulated for 20 min through the annular catheter flow cell system in vitro. Platelet adhesion onto the PSf porous catheter tube decreased sharply with increased saline solution perfusion rate. From the semilogarithmic relationship between the number of adhered platelets and perfusion rate, the critical perfusion rate for preventing adhesion of platelets could be about 0.3 ml min-1 cm-2. After the surface of PSf porous tubes was modified by non-ionic surfactant coating and air plasma treatment for 20 seconds without saline perfusion, the number of adhered platelets was lower than that of the control tube. These modification methods may be more effective in the prevention of initial platelet adhesion if combined with saline perfusion.