Serological methods are important in the study of the epidemiology and pathogenesis of Chlamydia trachomatis. However, their application in clinical diagnosis has been less successful. The microimmunofluorescence (micro-IF, or MIF) test is, so far, the only test that has an acceptable specificity and sensitivity. Other immunofluorescence tests and enzyme- and radioimmunoassays made available to date are of comparable sensitivity but present varying degrees of cross reaction to non-trachomatis chlamydiae, an entity whose prevalence currently is not known. The complement fixation (CF) test with the chlamydial group antigen is the least specific and sensitive method, and can only be applied in the diagnosis of deep chlamydial infections. The diagnostic value of the detection of antibodies in secretions of Chlamydia-infected individuals has not been finally evaluated.