The culture of two human strains of mycobacteria (H37Rv and H37Ra) on Sauton medium differs from that of a bovine strain (BCG) in the later phases of growth of the three strains. The yield of soluble non-dialyzable mycobacterial constituents extracted from the bacillary bodies is more elevated in the lag and the exponential phases of growth than in the later phases of growth. The appearance of mycobacterial constituents in culture filtrates of H37Rv and H37Ra occurs in two successive steps. The content of tuberculin in culture filtrates of strain BCG is very low.