Effects of intrarenal-arterial (i.r.a.) and intravenous (i.v.) infusions of PGE₂, I₂ and F_2α on systemic blood pressure (BP), heart rate (HR), renal blood flow (RBF), urine volume (UV), renal function and plasma renin activity (PRA) of the renal venous blood (RVPRA) were investigated. A dose-dependent fall in BP was observed with PGE₂ and I₂ and was accompanied by a tachycardia (PGE₂<I₂, i.r.a.<i.v.). PGE₂ and I₂ induced increases in RBF and UV in a roughly dose-dependent manner (PGE₂>I₂, i.r.a.>i.v.), however, antidiuresis was observed with the highest intravenously given dose of PGI₂ (300 ng/kg/min) such being ascribed to a pronounced hypotension. Changes in electrolyte excretion induced by PGE₂ and I₂ were similar to the pattern of those in RBF or UV. Neither PGE₂ or I₂ produced any significant changes in the glomerular filtration rate (GFR). The diuretic effect of PGE₂ and F_2α correlated with osmolar clearance (C_osm) (r=0.89, p<0.01 ; r=0.55, p<0.01) and free water clearance (C_H2O) (r=0.52, p<0.01 ; r=0.83, p<0.01), whereas that of PGI₂, only with C_osm (r=0.74, p<0.01). PGF_2α produced the weakest changes in the parameters described above. PGE₂ and I₂ (30 ng/kg/min, i.r.a.), but not PGF_2α, produced a significant elevation of RVPRA without any significant change in BP. These findings suggest that PGE₂ plays a primary role in the kidney, whereas PGI₂ is important in the regulation of the systemic circulation, and that PGE₂, I₂ and F_2α all have different modes of action in producing diuresis. Both PGE₂ and I₂ may participate in the control of renin secretion.