Most Angiotensin receptor blocker's (ARBs) are metabolized by cytochrome P4502C9 (CYP2C9), one of the major isoforms of the cytochrome P450 in human liver microsome. The purpose of this study is to evaluate whether CYP2C9 polymorphism has a significant clinical influence on the blood pressure lowering effect of losartan and valsartan. Weather there is a genetic importance in choosing the right ARB for the right patient.