Medical devices like catheters, hemodialyzers, oxygenators, heart valves, and blood vessel prostheses are frequently used in man as a consequence of natural and accidental causes of deterioration of his body. The formation of thrombi on the surfaces of artificial materials occurs upon contact with blood. Progress made over the last 25 years in the area of blood-biomaterial compatibility has been impressive. However, we still do not have a satisfactory thromboresistant material to replace a coronary artery.