Albino rats maintained for 50 to 60 days on rations containing cholesterol, sodium cholate, and thiouracil were found to be highly susceptible to the lethal effects of infection with Mycobacterium tuberculosis. Maximum loss of resistance occurred only when all three components were present in a single ration. A lesser degree of susceptibility resulted from the deletion of one or more of the factors from the diet. Animals maintained on control rations never died of the infection. Histopathological studies of stained sections of tissues of infected animals revealed that the reaction of the host to the bacillus was more extensive and less well contained in animals fed the complete atherogenic ration than in the controls.