We compared the effect of losartan (50 mg/day) to hydrochlorthiazide (12.5 mg/day) on blood pressure (BP) and arterial stiffness in 11 untreated hypertensive patients aged 47 to 69 years in a 4-week single blind randomized crossover study with an intervening 4-week washout period. Both drugs produced a significant (P <.001) and similar decrease in brachial BP. Only losartan induced a significant decrease in arterial wave reflection (P <.0001), with a preferential reduction in aortic (P <.001) compared to brachial pulse pressure. Losartan also significantly increased pulse pressure amplification and reduced pulse wave velocity. These results suggest that an AT(1) receptor antagonist induces a BP independent decrease in aortic stiffness and arterial wave reflection.