The response to warfarin varies greatly among individuals. Some of this variability can be ascribed to genetic polymorphisms in the gene encoding for CYP2C9, the enzyme mediating the metabolism of S warfarin. In addition genetic polymorphism in other genes (i.e. VKORC1, factor VII) have been shown to account for some of the variability in the response to warfarin irrespective of CYP2C9.The present study has several segments: