We report a comprehensive physicochemical characteriza-tion of a glycoglycerolipid from Mycoplasma fermentans, MfGl-II, in relation to its bioactivityand compared thiswith the respective behaviors of phosphatidylcholine (PC) and a bacterial glycolipid, lipopolysaccharide (LPS) from deep rough mutantSalmonella minnesotastrain R595. Theb«a gel-to-liquid crystalline phase transition behavior of the hydrocarbon chains withTc¼30 Cfor MfGl-II as well as for LPS exhibits high similarity between the two glycolipids. A lipopolysaccharide-binding protein (LBP)-mediated incorporation into negatively charged liposomes is observed for both glycolipids. .