In experimentally infected murine peritoneal macrophages and murine macrophage-like cells J-774 with different pathogen strains of tuberculos'is, Mycobacterium tuberculosis (MBT) underwent significant morphofunctional changes. In phagocytosis, several live and mycobacteria conventionally referred by the authors to as morphotype I cells come from the environment to the macrophage. Of them, single young and intact mycobacteria are able to multiply and form at 2-3 generations morphotype II microcolonies from 3-9 mycobacteria or more in the phasolysosomes within the first 24 hours after infection. Having taken the form of small-sized cocci and coccoovals having a closely packed cytoplasm, morphotype II cells can be long present intact in the phagocytes. By losing the cellular wall under the action of lytic phagolysosomal enzymes, single mycobacteria turned into L-form or morphotype III MBT. During damage and lysis in the macrophages, single mycobacteria can preserve a part of an intact cytoplasm and genome as ultraminor forms of mycobacteria or morpho-type IV MBT.