A number of methods are being developed to provide improved means to inhibit host activation by the foreign materials of circulatory assist devices. Surface treatments by heparinization, polymer bulk, and surface modification to inhibit or enhance protein film formation have all shown promise in this regard. These methods are applicable to a number of medical polymers. A brief review of the more promising of these methods is given. While a perfectly biocompatible surface is not yet on the horizon, we may nevertheless expect relief with these methods from the problems of bleeding, embolism, and general endothelial attack which currently provide substantial morbidity in circulatory assist procedures.