Immunization of animals against infections with Brucella sp. has been accomplished by employing living attenuated strains of Br. abortus as the antigen. Attempts have been made to immunize guinea pigs against brucella infections, employing as antigens killed organisms or fractions obtained by extraction. Huddleson (1) ground dried Brucella in distilled water and preserved the supernatant fraction obtained after centrifugation by addition of ethyl ether. Among 247 guinea pigs vaccinated with this material, only 9.0 per cent became infected while among 238 control animals 63.4 per cent became infected after receiving a challenge dose of Br. abortus. Live, Sperling and Stubbs (2) killed Br. abortus with ethyl ether and immunized guinea pigs with this material. Among 80 control animals 75 or 93.7 per cent developed brucellosis while among 43 animals vaccinated subcutaneously with the ether-killed vaccine 18 or 41.8 per cent became infected and among 17 animals vaccinated intracutaneously only 3 or 17.6 per cent became infected when given varying numbers of Br. abortus.