Recently results of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) showed that a thiazide diuretic was unsurpassed by any other drug class studied in achieving the level of cardiovascular protection, a finding reflected in the recent Seventh Report of the Joint National Committee on prevention, detection, evaluation, and treatment of high blood pressure (JNC7) recommendations. Oxidative stress has been found to be one of the key players in the pathophysiology of cardiovascular disease at large. The objective of this study was to check the hypothesis that diuretics may favorably affect the oxidative status of plasma, which could account in part for the results of recent trials.In addition to the routine workup in a series of 39 medically treated hypertensive patients, we analyzed the level of antioxidative protection afforded by the ferric-reducing ability of plasma (FRAP), according to class of drug used.We found that patients taking diuretics had significantly better antioxidative protection expressed by the higher levels of FRAP. Although the limited number of patients did not allow us to exclude the influence of other variables in the multiple regression analysis, we did not observe any differences in the level of FRAP when the group was divided according to the other drug classes, gender (men versus women), smoking, diabetes mellitus, duration of treatment, concomitant therapy, or level of uric acid.The use of thiazide diuretics seems to be associated with better antioxidative protection. This observation may add to the explanation of the results of recent trials in hypertension.