Antisera to Corynebacterium genitalium Types C-1 to C-6 were prepared in rabbits and the titers of complement fixing antibodies to the homologous strains, to the heterologous strains, to C. genitalium Types I to V, and to the reference species Corynebacterium xerosis and Corynebacterium minutissimum ascertained. Five Types stimulated low levels of cross-reacting antibodies to all corynebacteria tested including Type C-3. In contrast the antiserum to Type C-3 had antibodies to only two heterologous strains suggesting that these corynebacteria usually shared more than one minor cell wall antigen. The biologic reactions and serotypes of C. genitalium Types C-1 to C-6 have been compared with those of Types I to V. It is considered that C. genitalium should be retained for corynebacteria having the properties of Types I to V whereas corynebacteria having the characteristics of Types C-1 to C-6 that are commensals of the male and female urogenital tracts should be incorporated in a new species Corynebacteria pseudogenitalium sp. nov. The differences in the biologic characteristics of the two species have been discussed and summarized.