This review summarizes some basic properties and distribution of angiotensin I converting enzyme (ACE). ACE is one of several biologically important ectoproteins that exists in both membrane-bound and soluble forms. Localized on the surface of various cells, ACE is inserted at the cell membrane via its carboxyl terminus. Human plasma ACE originates from endothelial cells while other body fluids may contain ACE that originates from epithelial, endothelial or germinal cells. The two isoforms of ACE, the two-domain somatic form and the single domain germinal form, convert angiotensin I to angiotensin II, and metabolize kinins and many other biologically active peptides, including substance P, chemotactic peptide and opioid peptides. The broad spectrum of substrates for ACE and its wide distribution throughout the body indicates that this enzyme, in addition to an important role in cardiovascular homeostasis, may be involved in additional physiologic processes such as neovascularization, fertilization, atherosclerosis, kidney and lung fibrosis, myocardial hypertrophy, inflammation and wound healing. Future research should explore the possible functions of tissue ACE and its systemic role as a pressor agent. ACE inhibitors have achieved widespread use in the treatment of hypertension and the protection of endorgan damage in cardiovascular and renal diseases. Potential problems related to side effects and compliance of such therapy need to be adressed. A safer way of producing therapeutic effects is promised by the delivery of the ACE antisense sequences by a vector producing a permanent inhibition of ACE and long-term control of blood pressure in hypertensive patients.