Numerous studies have been carried out to assess the role of the renin system in sustaining abnormally high blood pressure and in contributing to various other cardiovascular disorders such as congestive heart failure, ascites, and shock. The clinical use of potent and specific inhibitors of the renin-angiotensin system has produced important application in the treatment of high blood pressure, severe congestive cardiac failure and experimental hemorrhagic shock. Only in the state of considerable sodium depletion does blockade of the renin system produce any untoward effect, i.e. hypotension. These results are very similar to those obtained previously in patients with bilateral nephrectomy. They raise the question whether under conditions of our present salt-eating habits the renin system is really necessary.