Direct renin inhibition is a new means for blocking the renin-angiotensin system at the rate-limiting step of the cascade of events triggered by renin release--the interaction of renin with its physiological substrate angiotensinogen. The remarkable success of angiotensin-converting-enzyme inhibitors and angiotensin receptor blockers in the management of cardiovascular and renal disease has led to great interest in the potential of direct renin inhibitors. This Review focuses on the evidence that suggests that direct renin inhibitors might block the renin-angiotensin system in the kidney more completely than either angiotensin-converting-enzyme inhibitors or angiotensin receptor blockers. The therapeutic implications of this evidence are also reviewed, as well as the possible mechanistic routes by which direct renin inhibition might exert its influence on the kidney.