Blood pressure, pulse rate, plasma aldosterone (PA), renin, and cortisol were monitored during graded intravenous infusions of prostaglandin At (PGA)1), 0.075-0.6 mug/kg min-1, alone and superimposed on angiotensin II (A II) administration in five normal men. The infusions of PGA1 did not affect blood pressure, but did progressively increase the pulse rate up to 15.2 +/- 2.0 (SEM- beats/min at the highest prostaglandin dose (0.6 mug/kg min-1). Both PA and plasma renin activity (PRA) increased in a dose-related fashion in response to the prostaglandin infusions. Aldosterone increased from a control of 4.8 +/- 0.4 to 20.7 +/- 1.2 ng and PRA increased from 0.9 +/- 0.1 to 5.4 +/- 0.4 ng/ml hr-1 at the dose of 0.6 mug/kg min-1. The correlation between the aldosterone and renin values was r = 0.85 P less than 0.001. In separate experiments, acute volume expansion with 2 liters of saline did not affect the increase in renin activity induced by exogenous prostaglandin. A II (5 ng/kg min-1) increased aldosterone and blood pressure and decreased the pulse rate. The hemodynamic effects were progressively reversed by the superimposed prostaglandin infusions, but the observed changes in renin and aldosterone concentrations were not further altered. The PA response to A II infusions was not influenced by indomethacin pretreatment. Prostaglandin A (infusion) appears to have a direct effect on renin release in man.