1. Bact. campestre, Bact. X, Bact. cucurbitae, Bact. pruni, and Bact. translucens var. undulosum were differentiated by direct agglutination tests with their antisera. 2. Cross agglutination so high that differentiation by the direct agglutination test was not possible occurred between antisera of Bact. phaseoli and the heterologous organisms Bact. X, Bact. cucurbitae, Bact. translucens, Bact. translucens var. undulosum, and Bact. Z; between the antisera of Bact. Y, and Bact. campestre; between the antisera of Bact. translucens, and Bact. translucens var. undulosum; and between the antisera of Bact. Z, and Bact. translucens var. undulosum. 3. Absorption of agglutinins was carried on with the cereal pathogens, and differentiated Bact. Z from the others; but, probably because of incomplete absorption, did not differentiate between Bact. translucens and Bact. translucens var. undulosum. 4. Even though the direct agglutination test did not differentiate all the organisms tested, consideration of all the recip...