The ultrastructure of Mycobacterium tuberculosis cells undergoing division was examined by electron microscopy. Two features of cell division were observed and are described here. First, cells are capable of undergoing a type of "snapping" postfission movement. This movement is likely due to a multi-layered cell wall in which the inner layer participates in septum formation while the outer layer ruptures first on one side. A second feature related to cell division is the ability of dividing cells to form transient branching structures.