Hypertension is a disease which affects over 26.4% of the world adult population, therefore novel approaches to the prevention and treatment of this disease need to be examined. Previous studies from our and other laboratories have shown that treatment of spontaneously hypertensive rats (SHR) and Dahl salt-sensitive rats with a renin-angiotensin system (RAS) inhibitor during the 'critical period' in hypertension development results in prevention of the later development of hypertension. In humans, Julius et al. reported similar findings in the landmark TROPHY study. Recently, we reported that 'pulse' treatment of SHR with high-dose angiotensin receptor blocker (ARB) is effective in causing sustained reduction of already established hypertension, even when the treatment was started after the 'critical period'. These results suggest the possibility that 'regression' of established hypertension may become feasible, and we have started a prospective, multicenter clinical study (STAR CAST study) to examine this possibility. In our animal studies, we found that treatment of rats during the 'critical period' with an ARB inhibits the development of renal arteriolar hypertrophy. Moreover, a high-dose angiotensin blocker caused a remarkable reversal of renal arteriolar hypertrophy in SHR, which was associated with changes in microvascular MMP expression. These results suggest that changes in the renal microvasculature may have an important role in the mechanisms of hypertension prevention and regression by ARB.