Motoneurons were directly visualized with Nomarski optics in slices prepared from new born rat spinal cord. Intracellular recordings from these neurons showed spontaneous potentials, probably triggered by interneuronal activity. Action potentials could also be evoked by direct intracellular stimulation of the motoneurons. Iontophoretically applied L-glutamate caused a fast depolarization of the motoneuronal membrane. Considerable differences in local sensitivity to L-glutamate were found on the surface of the motoneuron.