Microglial and astroglial cells undergo prompt responses to peripheral motor and sensory axon injury. These responses include proliferation of microglial cells as well as hypertrophy and increased levels of glial fibrillary acidic protein around the axotomized motoneurons and in the central projection territories of peripherally axotomized sensory ganglion cells. Proliferating microglial cells migrate towards reacting motoneurons, however, without directly apposing their cell membrane. Astroglial cells, on the other hand, increase their structural interrelationship with reacting motoneurons, seemingly at the expense of some presynaptic terminals. In sensory projection areas, microglial cells phagocytose degenerating axons and terminals. Beyond these observations, the functional role of the central glial cell response to peripheral nerve injury is obscure.