The numbers of people affected by treponemal diseases and the degree of resultant morbidity and mortality emphasize the need for improved methods for controlling these infections. The existence of identifiable infectious stages, the relatively low infectivity rates coupled with long incubation periods, the noninfectious nature of the latent stage, and the lack of a known animal reservoir make treponemal diseases good candidates for control by active immunization. The development of a practical, effective vaccine against the treponematoses is dependent on an understanding of the pathogenesis of the diseases, a knowledge of the immunologic mechanisms of resistance, a definition of the protective antigens, and a readily available source of these antigens. Recent contributions to our knowledge in these areas include the application of state-of-the-art techniques such as Western blotting, radioimmunoprecipitation, gene cloning, and monoclonal antibody production. The scope of potential vaccines, target populations, safety, and efficacy are topics of discussion.