The renin-angiotensin system maintains a homeostasis of blood pressure and blood volume. One component of this system is angiotensin-converting enzyme (ACE). There are two isozymes of ACE. The protein produced by vascular endothelium is termed "somatic ACE" and is regulated as a function of the growth state of these cells in vitro. The second isozyme, "testis ACE," is only produced by developing spermatozoa. The two ACE isozymes are the result of two distinct promoter regions within the ACE gene. Angiotensin II binds to specific receptors on the surface of cells. We have isolated cDNA encoding the AT1 subtype of receptor. This subtype is responsible for the hemodynamic consequences of angiotensin.