Fluorescent antibody methods were employed to study the antigens of intact Treponema pallldum, the "Relter treponeme", T. microdentium and T. zuelzerae, Veldkamp, a free living mud treponeme. Cross-fluorescent reactions were observed in every case. This was interpreted to mean that a shared or common antigenlc component is possessed by each of the treponemes. On the basis of absorption experiments, the common component was determined to be identical or similar to "Relter Protein Antigen". In addition to the fluorescein conjugates, antibodies to the shared antigen were found in test sera from both normal and syphilis donors. This suggests that antibodies of this type are probably nonspecific in nature both in respect to syphilis serology and treponeme identification. Absorption of fluorescein conjugates and test sera with intact Relter treponemes resulted in specific reactions.