The liver-specific autoantigen F was purified to monodispersity from man, beef, and mouse by conventional methods of protein chemistry. A negative version of immunosorption with Sepharose-bound rabbit anti-mouse liver immunoglooulins was partly successful. A molecular parameter (designated pIE) was worked out for direct comparison of anion-exchange data from the multiple forms of F antigens found in some of the species. Anion-exchange chromatography was the main tool for separating the multiple molecular forms differing in electrical properties.