Artificial insemination is a valuable method for facilitating genetic exchange between captive colonies of koalas (Phascolarctos cinereus) and for the maintenance of genetically important remnant populations. However, to reduce potential disease transmission, their semen needs to be screened for venereal diseases caused by organisms such as Chlamydia species. Semen samples from 11 koalas, eight of them with clinical signs of cystitis, were examined for the presence of Chlamydia by an optimised PCR assay. Chlamydia was detected in semen from seven of the 11 animals.