Mycoplasma fermentanshas unique glycoglycerophospholipids (GGPLs: GGPL-I and GGPL-III). Previously, the structure of these lipids was determined as phosphocholine-6′-α-glucopyranosyl-(1′-3)-1, 2-diacyl-glycerol (GGPL-I) and 1″-phosphcholine-2″-aminodihydroxypropane-3″-phospho-6′-α-glucopyranosyl (1′-3)-1, 2-diacyl-glycerol (GGPL-III). Thin-layer chromatography (TLC) immunostaining showed that the GGPLs were main lipid-antigens of theM. fermentansspecies. Anti-M. fermentansserum stained mainly the GGPLs, but the other anti-mycoplasma sera (anti-M. arginini,anti-M. hyorhinis,anti-M. pneumonia,anti-M. primatum,and anti-Acholeplasma laidlawii,anti-M. hominis,anti-M. orale,andM. salivarium) stained neither GGPL-I nor GGPL-III. The TLC analysis of glycolipids and phospholipids of various human related mycoplasmas showed clearly that GGPLs are specifically expressed inM. fermentansspecies. GGPL-I and GGPL-III ranged from 1.6 to 28% and from an undetectable level to 35% of total phospholipids, respectively. Although there was heterogeneity among the amounts of GGPL-I or GGPL-III ofM. fermentansstrains, all of theM. fermentansstrains had GGPL-I and/or GGPL-III. These observations showed that GGPL structures are species-specific immunodeterminants ofM. fermentans.The fact that the GGPLs are main phospholipid components of theM. fermentansspecies means theM. fermentanshas a unique choline metabolic pathway. This observation may raise phylogenetic interest.