Obtained were allergens from Brucella abortus 99 and Yersinia enterocolitica Type 9 through hydrolysis with hydrochloric acid after M. M. Ivanov and with acetic acid after Kirzhaev. They were tested on guinea pigs that were infected with Yersinia enterocolitica Type 9 through different ways. To M. M. Ivanov's allergens all infected animals responded pronouncedly in the case of the homologous allergen, and half of them only and to a lower degree in the case of the heterologous Brucella allergen. To Kirzhaev's allergens the infected guinea pigs showed more strongly expressed skin reactions. In this case, too, the response was stronger to the homologous Yersinai allergen. The diameters of skin swelling were more than twice greater than with the use of the heterologous Brucella allergen, and the sum of the reacting skin sites was five times greater in the case of the homologous Yersinia allergen. No essential differences were observed between the oral and the plantar route of infection combined with the subcutaneous injection of carboneum tetrachloratum and the morphine preparation Omnopon.