Human angiotensinogen has been purified from outdated blood bank plasma. The purified angiotensinogen has a specific angiotensin I (Ang I) content of 20.7 micrograms Ang I/mg protein and contains only one amino-terminal amino acid, aspartic acid. However, it exhibits two bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with apparent molecular weights of 61,400 and 65,400. It is concluded that these bands represent different forms of angiotensinogen because the specific Ang I content is equivalent to the theoretical Ang I content. Analysis of the purified angiotensinogen showed it to contain 14% carbohydrate.