Blood pressure reduction is the most significant factor in delaying onset and progression of renal disease. Blockade of the renin-angiotensin system (RAS) using angiotensin-converting enzyme inhibitors (ACEIs) delays renal disease progression. More recently, agents that block the RAS by preventing angiotensin II from binding to its subtype 1 receptor (ARBs) have been developed in an effort to prevent deleterious consequences of pathologic levels of angiotensin II and to reduce the adverse effects of RAS blockade associated with ACEIs. Human studies with a variety of ARBs have clearly demonstrated the antihypertensive and antiproteinuric efficacy of these agents in patients with progressive renal diseases. Moreover, the effects of ARBs are similar or identical to those of ACEIs. Ongoing long-term clinical trials are designed to determine whether ARBs also preserve renal function similar to ACEIs. Specifically, the role of ARBs in patients with hypertension and type 2 diabetes is being evaluated in 3 large trials, including Appropriate Blood Pressure Control in Diabetes-Part 2 With Valsartan, the Losartan Renal Protection Study, and the Irbesartan Diabetic Nephropathy Trial. Definitive evidence of the long-term protective effects of ARBs in chronic progressive renal disease is expected from these important studies.