IMMUNOCHEMICAL studies carried out by D'Alessandro et al. 1 on a non-pathogenic, culturable treponeme, the so-called Reiter treponeme, revealed the presence of four antigenic components: (1) a thermolabile protein; (2) a specific, thermostable antigen with polysaccharide characteristics; (3) a lipoid, corresponding to the ubiquitous lipidic antigen cardiolipin; (4) another lipoid similar to the organ-specific cerebral antigen of Witebsky2. These studies led to the conclusion that the treponemes, like other organisms, are mosaics of antigens, and a safe basis was established for a better understanding of the complex serological response of the infected host.