Serological grouping of Veillonella alcalescens strains isolated from the alimentary tract was performed by cross agglutination. There were complicated antigenic relationships among these strains, which were divided basically into two groups. One group consisted of strains of rumen origin and the other of strains of lower alimentary tract origin.
When Veillonella alcalescens was examined for antigenic structure, it possessed heat-labile antigen in addition to somatic antigen. Furthermore, it was clarified that formolized antigen was closely related to heat-labile antigen. This heat-labile antigen corresponded to K-antigen of enterobacteria. It resembled C-type antigen found in Proteus, but did not resemble B-type antigen of Neisseria gonorrhoeae.