We examined the chronic effect of aluminum on the rabbit central nervous system (CNS) and documented the occurrence of axonal swellings (spheroids) and dendritic thickening in spinal cord neurons in addition to the accumulation of neurofibrillary material in the perikaryon. The axonal swellings always occurred at the first heminode, and the neurofilaments appeared disorganized, whereas in dendrites the neurofilaments generally retained their longitudinal arrangements. Although neurofibrillary tangles were present in cortical neurons, no axonal swellings were observed. Thickening of segments of apical dendrites proximal to the cell body affected by neurofibrillary changes was present. The axonal swellings resembled those observed in IDPN intoxication, and in amyotrophic lateral sclerosis, and may be useful as a model for studying these diseases.