As the causative agent of the common sexually transmitted disease syphilis and a fastidious, microaerophilic obligate parasite of humans, Treponema pallidum subsp. pallidum is one of the few prominent infectious agents that has not been cultured continuously in vitro. T pallidum therefore represents an attractive candidate for genomic sequencing. Preliminary sequence results from the 1.13 million base pair genome are consistent with the expected limited metabolic capabilities of this spirochete, but indicate that the bacterium may express toxins and surface proteins that have not been identified previously.