To establish a method for the detection of Chlamydia species-specific antibodies to the three species of Chlamydia responsible for human disease, the author attempted to remove Chlamydia genus-specific antibodies by prior adsorption with heterologous Chlamydia antigen. The effects of adsorption with heterologous antigen were investigated by the microplate immunofluorescence antibody technique. The Chlamydia genus-specific antibodies in immune animal sera were significantly reduced by prior adsorption with heterologous Chlamydia antigen. Chlamydia pecorum which does not infect humans was found to be useful for the adsorption. A preliminary test using Chlamydia trachomatis-infected human sera showed that this adsorption method with C. pecorum is applicable to the serodiagnosis of human Chlamydia infections.