The effects of a continuous intravenous infusion of prostaglandin E1(PGE1) on mean arterial pressure (MAP), sodium and water balance, and plasma renin activity (PRA) were examined in 10 conscious dogs maintained on a 70 to 75 mEq/day sodium intake. In a crossover pattern, each dog received 6 days of intravenous PGE1(0.1 μg/kg/min) and 6 days of intravenous diluent. When compared to diluent, intravenous PGE1resulted in a mild sustained rise in MAP. By Day 6 the intravenous PGE1, MAP had increased from 98 ± 4 to 112 ± 5 mm Hg (mean ± SE) (p< 0.04). Concurrent with the MAP increase, PRA increased from 0.6 ± 0.2 to 3.1 ± 0.7 ng angiotensin I (AI)/ml/hr (p< 0.03). To assess the role of the renin-angiotensin system in the maintenance of the systemic hypertension, AI converting-enzyme inhibitor was given to four dogs on Day 6 of both intravenous PGE1and diluent. Only when the dogs were receiving PGE1did the administration of convertingenzyme inhibitor result in a significant decrease in MAP (− 19 ± 5 mm Hg). In addition to increasing arterial pressure, the chronic infusion of PGE1also produced changes in salt and water balance. When compared to diluent, PGE1resulted in a twofold increase in both water intake and urine output, an increase in urinary sodium excretion (from 72 ± 3 to 84 ± 6 mEq/day,p< 0.05, on Day 1), and a decrease in urine osmolality (from 942 ± 82 to 586 ± 61 mOsmol/kg H2O/day,p< 0.05, on Day 1). We conclude that, in the dog, a 6-day intravenous infusion of PGE1results in rerun-supported hypertension and increased water intake, urine output, and urinary sodium excretion.