The purpose of this study was to assess the participation and interaction of the renin-angiotensin system and vasopressin in the early stages of the development of salt-induced hypertension. Subtotally nephrectomized rats, fed 1% saline, were treated over a 10-day period with either an antivasopressor V1 antagonist (by osmotic minipump) or an angiotensin converting enzyme inhibitor (either captopril or ramipril, given daily by oral gavage), or a combination of the two modes of treatment. Surprisingly, only ramipril (either alone or in combination with the V1 antagonist) could prevent the development of hypertension in these animals. Our data would not permit conclusion as to whether the different capacity of these agents to prevent salt-induced hypertension was due to a different degree of penetration into the central nervous system, or to some other property.