The multi-epitope cocktail detects the elementary bodies (Ebs), reticulate bodies (RBs), intermediate forms, chlamydial inclusions and specific cell-associated antigen(s) directly in samples. The conjugate is used for direct immunofluorescence staining combining three specific monoclonal antibodies (mab) conjugated to fluorescein isothiocyanate (FITC). One mab is specific for the genus-specific epitope located on the Chlamydia LPS and identifies all the 15 known serovars of C. trachomatis as well as C. psittaci and C. pneumoniae by displaying bright fluorescence of intracellular inclusions and pin-point shaped extracellular organisms as well as free cell-associated chlamydial antigen(s). A second mab reacts with an epitope on the Chlamydia outer membrane complex protein (60 kD) and shows preferential fluorescence around the periphery of individual RBs of all serotypes of C. trachomatis and of C. psittaci strains; this antibody also stains the EBs of C-complex serovars as pin-point shaped structures. The third mab identifies a species-specific epitope on the major outer membrane pro- tein (40 kD) and shows brilliant fluorescence with EBs, RBs and cytoplasmic inclusions of B-complex serovars of C. trachomatis, whereas C-complex serovars show medium to weak fluorescence. The combination of these 3 specific mabs provides uniform and intense staining of all the stages in the developmental cycle of the known C. trachomatis serovars (A–C, D–K, L1–L3) and C. psittaci and C. pneumoniae strains. A positive cross-reactivity was also reported for Chlamydophila pecorum.