Ex vivo production of IFN-gamma, TNF-alpha, and IL-6 by mouse peritoneal macrophages was studied during successive infection with the vaccine strain M. bovis BCG and virulent strain M. tuberculosis H37Rv. The increase in the concentrations of TNF-alpha and IL-6 did not depend on the sequence of macrophage infection with the vaccine or virulent strain, but was related to the presence of the vaccine strain M. bovis BCG in the medium. IFN-gamma production depended on infection of macrophages with the virulent strain M. tuberculosis H37Rv. The concentration of IFN-gamma was maximum during primary infection with the virulent strain and did not increase after successive infection with the virulent and vaccine strain.