The present experiments have allowed the calculation of concentrations of angiotensin I, II, and III in arterial and central venous blood. Assuming that endogenous arterial angiotensin II and III are handled as reflected by exogenous infusion, it can be calculated that 55% of the steady state arterial concentration of angiotensin II has arisen in passage across the peripheral vascular bed, that 40% of angiotensin III is also produced there, and that the arterial concentration of angiotensin III is 42% of the arterial concentration of angiotensin II.