Motility seems to be required for an intimate association with the intestinal mucosa which is necessary for efficient toxin delivery in the pathogenicity of V. cholerae. 2) A vaccine of semipurified flagella (CF) afforded a high degree of active and passive immunity in the rabbit ileum to both homologous and heterologous challenge strains. 3) The nature of the immunoglobulin type involved in the active immunity elicited by CF was not clear but preliminary indications implicate both s-IgA and IgG.