The optic nerve consists of axons, glia, and undifferentiated cells; neuronal cell bodies are absent. To study the developmental potential of glia and precursor cells in vitro, we devised an original, long-term culture system of optic nerve explants, called minisegments, of newborn rats; at this stage the nerves are composed of naked axons, astrocytes, and undifferentiated cells. After about 4-5 weeks in culture, neuron-like cells appeared, which showed morphological, fine structural, and immunocytochemical properties ascribed to neurons. These neuron-like cells may be derived from a common neuron-glia progenitor or from a small population of precursors, which never produce glia in situ.