Chlamydia are common agents of sexually transmitted diseases and in this country more frequent than Neisseria gonorrhoeae. Approximately 10% of all infections with chlamydia trachomatis are followed by complications, which can lead to infertility and other sequelae. Therefore, early recognition of the infection and subsequent effective therapy are important. The dermatologist is often the first physician consulted and the outcome of the infection may depend on his diagnostic and therapeutic measures. The experienced microbiologist can provide an etiologic diagnosis. For this, isolation of Chlamydia trachomatis in optimally performed tissue culture still is the most sensitive and specific method. Currently available commercial IF- and ELISA-tests for direct detection of the agent in secretions are less sensitive and less specific.