Minor head injury or concussion was produced in experimental animals by an acceleration-deceleration non-impact injury. The animals sustained a brief loss of consciousness and no sequelae were observed. The brains were examined at 7 days by means of the Nauta and Fink-Heimer techniques. Degenerating axons were noted in the inferior colliculus, pons, and dorsolateral medulla. Degeneration was not seen in the subcortical white matter, thus suggesting a primary brain-stem locus for concussion. These findings also suggest that, in some instances, minor head injury or concussion can be associated with organic damage to the central nervous system.