With the purpose to elucidate the in vivo antigenicity of homologous animal organs, especially of the liver, and also to clarify the problem centering around the visceralspecificity and the harful effect of the homologous liver antiserum obtained from the same species of animals sensitized with the homologous animal antigens, the author carried out serological investigations, and obtained the following results. 1. Antigenicity can be recongized in the liver of the same species of animals, but its antibody titer is lower than that of different species of animals; and moreover, the in vivo reactions between such a liver antiserum and various visceral antigens of rabbits reveal a relative visceral specificity. 2. When the same species of animal is sensitized with antigen extracted from the rabbit liver, homologous liver antibody can be detected not only in the circulating blood but also in various organ tissues of the rabbit. 3. When the homologous liver antiserum obtained from the same species of animal sensitized with the antigen extracted from rabbit liver is inoculated into the same species of rabbits, disturbances in the liver and neighboring internal organs can be recognized serologically and functionally. Moreover, the serum of such animals possesses the relative visceral specificity.