In this study, the influence of hydrochlorothiazide on pharmacodynamics and pharmacokinetics of losartan was studied using human hypertensive patients. A total of 135 hypertensive patients were included in this study. The reduction in the blood pressure in patients receiving the Losartan alone and in patients receiving the both Losartan and hydrochlorothiazide was estimated. The pharmacokinetic parameters also estimated using the plasma levels of Losartan in both group of patients. The findings of present investigation have concluded that the efficiency of Losartan along with the Hydrochlorothiazide was high when compared to that of Losartan alone, and preliminary pharmacokinetic data also revealed that there were no interactions with the usage of combination of drugs.