Chlamydia trachomatis, the species most frequently found in sexually transmitted disease, is dangerous because of potential complications associated with infection: endometritis, salpingitis, ectopic pregnancy and sterility in adults, and conjunctivitis and pneumopathies in the newborn. C. psittaci, which is less frequently found in man and is transmitted primarily from birds, can cause pneumonia. C. pneumoniae also causes acute and chronic respiratory diseases, and has been associated with cardiovascular disease as well. IgG antibodies are elevated during respiratory infections and in chronic genital infections or reinfections. The Platelia Chlamydia IgG antibody test is useful for determination of an individual’s immune status against Chlamydia species (single specimen) or recent infection (when paired sera are available).