Many types of polymers have been used for medical devices for blood contacting application. Polyurethanes have been determined to be one of the more blood-compatible. However, there is variability within types of polyurethanes and even within the same type of polyurethane as far as hemocompatibility. This variability stems in part from differences in processing aids, including waxes, which manufacturers add. An understanding of the surface chemical properties is essential for the determination of the hemocompatibility of polyurethanes. For this presentation, we describe analysis of the wax component of the surface of a polyurethane commonly used for extruded medical devices, Pellethane 2363 (Dow), by Fourier-transform infrared-attenuated total reflection (FTIR-ATR) and x-ray photoelectron spectroscopy (XPS), and the effect of its presence on the hemocompatibility of Pellethane. Solvent cleaned samples, demonstrating reduced amide processing wax component by the two techniques, are also evaluated for blood-surface interactions. Tubing samples are evaluated for hemocompatibility by exposure to human platelet/plasma solutions followed by analysis using scanning electron microscopy. There is a direct correlation between the amount of amide processing wax in Pellethane as determined by FTIR-ATR and XPS and the in-vitro hemocompatibility.