The occurrence of bovine ephemeral fever virus has been reported from South Africa, Australia and Japan (Andrewes & Pereira, J 967) . The similarity of the symptoms caused and the sensitivity of the South African and Australian viruses to ether and desoxycholate suggest that the same virus occurs in all these countries. Electron microscopic studies on the South African form (EF 1) (Lecatsas, Theodoridis & Erasmus, 1969) have shown the virus to be cone-shaped . Jto, Tanaka, Inaba & Omori (1969) have published electron micrographs which indicate that the Japanese form (bovine epizootic fever) is bullet-shaped. The Austra lian fo rm (7721) has not, to our knowledge, been characterized morphologically as yet. In this communication are presented electron micrographs of the three viruses grown in BHK21 cells and a comparison is made in the structure of the virus particles as they appear in thin section and in negative contrast. Cross neutralization tests using the three virus strains are also reported. Our methods of preparation of material for electron microscopy a re described in the accompanying article in this journal (Lecatsas, Erasmus & Els, 1969). Susceptible bovines were used for the preparation of immune sera. The Australian strain (7721)* was derived from the second passage in BHK21 cells, the Japanese stra in (bovine epizootic fever)** was derived from the 23rd passage in BHK21 cells and the South African strain (EF 1) was derived from the 19th passage in BHK21 cells. All the animals received two inoculations intramuscularly of 2 ml antigen adsorbed to an eq ual amount of aluminium hydroxide. The second inoculation was given 21 days later. The immune sera were collected four weeks after the first inoculation. Neutralization tests were performed in day-old suckling albino mice. Plate 1 shows the three virus strains in section and negatively sta ined . Morphologically, it appears that the Austral ian and Japanese varieties are bulletshaped particles closely resembling the virus of vesicular stomatitis. The South African form, however, is morphologically different being cone-shaped and larger in basal diameter. It is noteworthy that no cone-shaped particles could be found in the Australian and Japanese strains and no bullet-shaped forms could be foun d in the South African variety. Thus, on the basis of morphology the Australian and Japanese forms appear to be similar. Distribution of electron dense material in the virus particles appears to differ in that the conical form shows a relatively electron-