1. The transfer of type K. colicinogeny to Shigella sonnei Phase II has been described.
2. The colicine elaborated by this microorganism is a lipopolysaccharide-protein complex which resembles the somatic antigen of the noncolicinogenic parent.
3. Although the colicine K of Escherichia coli K235 and of Sh. sonnei differ both chemically and serologically, they resemble each other in that both elicit type K colicine-neutralizing antibodies and both have the same bactericidal specificity.
4. The nature of the chemical changes brought about in the somatic antigen of Sh. sonnei through the acquisition of colicinogeny remains unknown