The systemic and renal hemodynamic effects of PLV-2 (octapressin) were studied in patients with hypotension or decompensated cirrhosis of the liver. Low doses (0.004 to 0.02 units/min) increased renal blood flow (indicator-dilution technique), reduced renal vascular resistance, and produced a slight increase in arterial pressure and systemic vascular resistance. Higher doses (0.1 to 0.5 units/min) produced a sharp increase in arterial pressure and systemic resistance while renal resistance increased moderately and renal blood flow usually was maintained above control levels. Renal fraction was increased at all dose levels. The increased renal blood flow was accompanied by more rapid intrarenal dye transit time and slight increase in renal extraction ratio of paraaminohippurate suggesting a rise in cortical blood flow. It is concluded that PLV-2 in small doses produces renal vasodilation and in larger doses preferential extra-renal vasoconstriction resulting in redistribution of blood flow to the kidney.