We have prepared and purified a rabbit polyclonal antibody (PcAb) and two mouse monoclonal antibodies (McAbs) against human angiotensinogen. The PcAb (Kd: 4.0 X 10(-12) M) inhibits 50% of the hydrolytic activity of renin on angiotensinogen, at a final dilution of 1:800. The two monoclonal antibodies (Kd: 5.0 X 10(-11) and 9.0 X 10(-13) M) do not inhibit the enzymatic reaction. None of the antibodies showed displacement of 125l-labeled angiotensinogen by angiotensin I, angiotensin II or human tetradecapeptide. The polyclonal antibodies recognize marmoset and baboon angiotensinogen with an affinity 10(3)lower than that of the human angiotensinogen, whereas the McAbs do not recognize primate angiotensinogen. Since the two monoclonal antibodies recognize different epitopes of the human angiotensinogen molecule than the polyclonal antibody, it is therefore possible to use them in various sandwich assays as ELISA. Thus, we have developed a liquid phase radioimmunoassay and an ELISA which allowed to measure human plasma angiotensinogen, under several pathophysiological conditions, and that produced by human hepatocyte cells in culture (HepG2).