The surface and blood compatibility characteristics of Pellethane polyurethane blended with 1% or 5% (w/w) polytetramethylene oxide (PTMO) were evaluated. Analysis by X-ray photoelectron spectroscopy indicated that blending of PTMO caused an increased amount of amide wax, a processing agent present in Pellethane, to be expressed on the surface of the blended films in vacuo. Dynamic contact angle measurements in water, however, showed that PTMO was preferentially expressed on the blend film surfaces in water. The two lower molecular weight species, PTMO and amide wax, were thus capable of reorienting, depending on the environmental conditions. An in vitro assay of platelet adherence and thrombosis showed that polyurethane blended with 5% PTMO had about two-thirds fewer adherent platelets compared to unblended polyurethane and that a blend containing 1% PTMO was intermediate in platelet adherence. Measurements of albumin adsorption from binary solution with fibrinogen indicated that PTMO blends did not preferentially adsorb albumin compared to unblended polyurethane.