Up to 10 glycolipids were detected in F. tularensis with the use of thin-layer chromatographic techniques. These glycolipids were slime antigens of F. tularensis membrane. Attenuated F. tularensis strains were found to have defects in their glycolipid composition: in the vaccine strain glycolipid 8 was replaced by more polar lipid 8-a; the avirulent strain had only two glycolipids, and one of them was not typical for virulent strains. Considering that glycolipids differed from entero-bacterial Vi-antigen in their physical-chemical and biological properties, the suggestion was made that the use of the symbol "Vi" to denote the surface substances of F. tularensis should be abolished.