Youmans, Anne S. (Northwestern University Medical School, Chicago, Ill.), and Guy P. Youmans. Effect of mitochondrial stabilizers on the immunogenicity of the particulate fraction isolated from Mycobacterium tuberculosis. J. Bacteriol. 87:1346-1354. 1964.-A number of substances which have been used to stabilize mammalian mitochondrial preparations were tested to determine whether they would similarly affect the immunogenicity of a particulate fraction prepared from ruptured viable attenuated mycobacterial cells. The use of 0.44 m sucrose and the presence of 3 x 10(-2)m MgCl(2) during the preparatory processes markedly increased the immunogenicity of the particulate fraction. The increase was so great that immunogenic preparations were then consistently obtained which, in adequate dosage, were more immunogenic in CF-1 male mice than were viable attenuated mycobacterial cells. On the other hand, adenosine triphosphate (ATP), citrate, and polyvinylpyrrolidone when present during the preparatory processes reduced the immunogenicity. The addition of MgCl(2), ethylene-diaminetetraacetate, or ATP to the particulate fraction after it had been prepared did not increase its immunogenicity. When the particles were prepared in the 0.44 m sucrose buffer alone, incorporated in Freund's adjuvant, and injected intraperitoneally, immunogenicity was increased. However, this increase was not significantly greater than that obtained when the particles were prepared in the sucrose buffer containing MgCl(2). The immune state engendered in mice by the intraperitoneal injection of the particulate fraction persisted for at least 12 weeks.