Many hormonal systems are involved in salt homeostasis and blood pressure control, including the renin-angiotensin-aldosterone system, the kallikrein-kinin system, and atrial and brain natriuretic peptides. Many of these hormonal peptides have actions both in the central nervous system and the periphery that are complementary. There is also increasing evidence that many of them may act as both circulating endocrine systems as well as local paracrine autocrine systems. The atrial natriuretic peptides may be viewed as endogenous inhibitors of the renin-angiotensin system. Angiotensin-converting enzyme (ACE) and renin inhibitors have provided important information on the role of the renin-angiotensin system in physiological and pathophysiologic states. The development of specific atriopeptidase inhibitors, kinin antagonists, and kallikrein inhibitors offer the same promise for these systems.