Artificial transformation of the O antigen of Salmonella group E (O-3.10 •¨ O-3.15 ; O-3.15•¨O-3.10 ; O-1.3.19•¨O-3.15) with antiserum has been reported by Bruner & Edwards (1948), Obara (1950), and Uetake (1952). Iseki and Sakai (1953 a, b) reported that antigenic transformation of subgroup E1 into E2 could be made only by the autolysate derived from strains of subgroup E2. Investigating the antigentransforming agent, they found that the strains of subgroup E2 are lysogenic and