Chlamydia trachomatis serovars A-L3 are the causative agents of hyperendemic blinding trachoma, a largely neglected disease of the developing world, and sexually transmitted infections that are epidemic world wide and a major cause of salpingitis. Trachoma is afflicts an estimated 200 million people and SDI are epidemic worldwide causing salpingitis an important cause of pelvic inflammatory disease (PID) tubal factor infertility (TFI). Control of these important human diseases is the long term goal of this project. Towards this end our goal is to develop a safe and efficacious vaccine to prevent chlamydial disease. The obligate intracellular life style, complex developmental biology, and antigenic structure of chlamydiae have severally hindered progress in vaccine development. A major hurdle in chlamydial vaccine development has been the unavailability of antigens capable of providing broadly reactive protective immunity against the multiple serovariants (15) that cause oculogenital infections. The immediate goal of this work was to identify such antigen(s), (ii) characterize them as targets of neutralizing antibodies, and (iii)generate recombinant antigen and infectious vectors expressing recombinant antigen that can be experimentally tested as vaccines in pre-clinical models of infection and disease.