Now that it is realized that the chemotherapy of tuberculosis has not been as successful as had been hoped, attention is again being directed to the possibility of anti-tuberculosis vaccination. As a result, this analysis of the tuberculosis problem gains an added timeliness. Dr. Max Lurie, one of the foremost researchers in the field, presents a documentation and integration of forty years of investigation into the nature of native and acquired resistance to tuberculosis, together with a critical survey of much of the past and current literature on the subject. Interpretation of the experimental observations led to the formulation of unified concepts which may underlie the mechanisms of resistance to tuberculosis and the mode of action of some of the body forces which affect these mechanisms. In view of the present emphasis on molecular biological research, these new concepts promise a deeper understanding of the defensive mechanisms in resistance to infections in general and to tuberculosis in particular.