Polyurethanes containing z-lysine segments in the main chain (PULL) were synthesized from 4,4'-diphenylmethyl diisocyanate, poly(tetramethylene glycol), and z-lysine oligomer as a chain extender. PULL film was treated with a 10%, HBr-acetic acid solution and subsequently with a saturated sodium bicarbonate aqueous solution to produce a primary amine group on the surface. Heparin-immobilized PULL (PULL-H) was prepared by the coupling reaction of PULL surface amine groups and heparin carboxylic acid groups. The surface-modified PULLs were then characterized by attenuated total reflection-Fourier transform infrared spectroscopy, electron spectroscopy for chemical analysis, and a contact angle goniometer. The concentration of amine groups and heparins introduced on the PULL surfaces were about 2.1 mumol/cm(2) and 1.9 mug/cm(2), respectively. To assess in vitro blood compatibility, the interaction of modified PULLs with plasma proteins and platelets was examined. In the experiments with plasma proteins, plasma recalcification time and activated partial thromboplastin time were significantly prolonged on PULL-H compared to those on the other surfaces. The percentage of serotonin released from platelets adhering on PULL-H was less than that on the other surfaces, demonstrating a good in vitro blood compatibility. (C) 2003 Wiley Periodicals, Inc.