SUMMARYMethods are described for the preparation of cell-wall material and flagella from Vibrio fetus. In common with certain other Gram-negative organisms V. fetus apparently possesses a three-layer wall which, it is proposed, consists of an outer lipoprotein layer, a middle lipo-polysaccharide layer, and an inner mucopeptide layer. These layers were studied chemically and by electron microscopy after various extraction and enzymic degradation procedures with whole-wall material. None of the layers of the wall was found to possess a microscopically discernible substructure, although the extracted lipopolysaccharide agglomerated into a characteristic stringy array. The probable function, contribution to cellular rigidity, and composition of the wall layers is discussed.