The Crabtree effect, considered an inherent peculiarity of the majority of malignant tissues, was found in all examined strains of Escherichia and Proteus and was absent in Micrococcus and Serratia. The maximal value of the Crabtree effect in E. coli cultures occurred at the time of the initial period of log multiplication. The finding of the Crabtree effect in the examined bacteria strains indicates an analogy existing between the metabolic behavior of malignant tissues and certain facultatively anaerobic bacteria.