A single strain ofBacteroides nodosuswas cultured under controlled conditions on hoof agar or in either biphasic medium or hoof broth. The gross and ultrastructural appearances of organisms were compared one with the other and withB. nodosusas seen in necrotic detritus obtained from a case of non-progressive foot rot. The possible imphcations of those morphological differences with regard to the antigenic structure of cells and their suitability for vaccine production, are briefly discussed.