Cellular and fibrillar organization of the hypothalamic (HLR) and mesencephalic (MLR) locomotor regions of the brain stem has been studied in cats by means of staining the nervous tissue after Nissl and Sokolyansky. Morphometric investigations of neurons in these regions has been performed in frontal and sagittal slices. Within the limits of the HLR ad MLR there are about 45,000 of neurons, which are organized as various nuclei, the MLR cells arranging in them more compactly in comparison to diffusely ++ scattering HLR neurons. Within the limits of the locomotor regions, together with the cells and powerful compact fasciculi of fibers in the tract passing, that is especially specific for MLR, there are also numerous diffusely ++ scattered fibers. A possible role of the neurons and the fibers passing in starting locomotion at activation of the locomotor areas of the brain stem is discussed.