Bacteria within the genus Chlamydia are obligate intracellular parasites. There are three species within the genus. Chlamydia trachomatis causes trachoma and sexually transmitted diseases among humans. C. tra chomatis is comprised of three biovars: tra choma, lymphogranuloma venereum and murine [1]. C. psittaci is a common pathogen of avian species and domestic mammals. Speciation within the genus has been limited by lack of appropriate taxonomic tools. It is clear that C. psittaci contains many different microorganisms. This discussion will be re stricted to these two organisms as the re cently described C. pneumoniae (also known as TWAR strains) has been insufficiently studied to allow meaningful discussion [2].