The process of differentiation of neurons was traced on an organotypic cerebellar culture of newborn mice. Cerebellar cells reach morphological maturity by the 18-21st day of culturing. An increase of the membrane potential begins on the 6-7th day of culturing. It reaches values characteristic for the definitive stage of the neuron (65-75 mV) by the 9-10th day of culturing. Spontaneous action potentials begin to be recorded on the 10-12th day of culturing. At this time they markedly differ in their characteristics from the action potential of the mature neuron. The differences become less noticeable by the 16-18th day of culturing. However, final maturation of the action potential occurs at later times. The formation of specific sensitivity of cerebellar neurons to acetylcholine correlates with the time of formation of the action potential. © 1986 Plenum Publishing Corporation.