Anti-Human IgG (goat IgG) is often used as a secondary antibody for the detection of Human IgG. Following recent advances in the development of antibody-based therapy, such as the development of Human antibodies, this secondary antibody has been used for the purpose of investigating metabolism in the living body following administration of this antibody. In studies using monkeys, conventional anti-Human IgG (goat IgG) antibody tends to cross-react with the monkey’s own antibodies and that makes it difficult to achieve highly specific detection of the administered antibody. To overcome this problem, we have incorporated the additional step of absorption with monkey IgG. This antibody is expected to minimize non-specific reaction even when it is used for ELISA with monkey blood samples, and also make it possible to detect the human antibody in a concentration range that is difficult to detect with conventional secondary antibodies.