The essentials of experimental results as well as the present views by previous authors on the anatomical localization, functional and neuronal organization of the respiratory centers were critically reviewed. In aiming to obtain more pertinent evidences on the anatomical localization, the functional and neuronal organization of the central respiratory mechanisms in the brain stem of the cat and rabbit, the different 10 series of experiments were undertaken. In the present review the experimental results concerning with changes in spontaneous unitary discharge pattern of the pontine and a bulbar respiratory neuron with simultaneous recording of both unit activities before and after brain stem transection at the ponto-bulbar junction were described and their physiological significance was discussed. Based on these experimental results a model of the neuronal organization of the central respiratory mechanisms in the brain stem consisting of 4 subsystems of respiratory neurons; a primary; a satellite; an input; and an output neuron system, was proposed.