The thromboresistance of 13 potentially blood-compatible polymers was assessed in sheep by determining survival of5lCr-labeled platelets. Polymer tubing (120-150 cm x 2.0-2.3 mm i.d.) coiled around the neck was incorporated into the circulation through silicone rubber connectors as a carotid artery-external jugular vein shunt. The mean platelet half-life in control animals ("shunt control") was 78.2 ± 2.8 (SEM) hours. Eleven of the 13 polymers tested significantly shortened platelet half-life. Polyvinyl chloride (T½= 45.4 ± 3.0 hours), polyperfluoro ethylene (T½= 47.0 ± 1.6 hours), and a polymethyl acrylate (PMA)/acrilonitrile copolymer (T½= 50.7 ± 7.0 hours) produced the greatest shortening. Only silica-free polydimethyl siloxane (T½= 74.7 ± 4.9 hours) and PMA (T½= 81.5 ± 3.4 hours) were indistinguishable from shunt controls. Pretreatment of PMA tubing with autologous plasma in a paired trial significantly increased platelet half-life (P< 0.05 vs. untreated PMA). This system offers an economical, reproducible, sensitive, and biologically relevant method for assessment of the reactivity of artificial surfaces with platelets. Circ Res 46: 84-90, 1980