The purified elementary bodies (EBs) of C. pneumoniae ATCC VR1310 were used for primary immunization of male BALB/c mice (8 weeks of age), with the boost following on day 14. Spleen cells were fused with murine myeloma NS-1 cells on day 24 and hybrid cells were cloned by limiting dilution. Two clones, P17C2 & P33C, secreting species-specific monoclonal antibodies (MAbs) and immunoglobulin IgG2a class were obtained after elimination of those clones that produced antibodies against C. trachomatis L1, L2, A, B, C, E serovars, C. psittaci EAE strain and uninfected BGMK cell antigens. It was showed that the two clones of MAbs reacted with the MOMP 39.5 x 10(3) Da major outer membrane protein of all chlamydia species in Western blot and their ascites titers were more than 1:25 600 in Micro-IF test.