In the present study, we performed immunohistochemical techniques to investigate the changes in ubiquitin expression in the central nervous system of the transgenic mice expressing a human superoxide dismutase 1 mutation (SOD1)G93A. Sections of brains from control mice showed virtually no immunostaining for ubiquitin, whereas sections from SOD1G93A transgenic mice contained numerous granular or linear deposits of ubiquitin. A high density of the processes containing ubiquitin was detected all around the gray matter of the spinal cord of the mutant transgenic mice. Ubiquitin immunoreactivity was also detected in the cerebellum, brainstem and midbrain of transgenic mice. The first demonstration of the distribution of ubiquitin in the whole brains of the transgenic mice may provide clues for understanding the neuronal degeneration mechanism in amyotrophic lateral sclerosis and other neurodegenerative diseases.