Using monoclonal antibody (Ta-51) that specifically binds phosphorylated high molecular weight neurofilament (pNFH) proteins, we investigated the occurrence of perikaryal pNFH in the spinal ventral horn motoneurons, intermediolateral column (ILC) neurons, sympathetic ganglion neurons and dorsal root ganglion (DRG) neurons obtained from patients with amyotrophic lateral sclerosis (ALS) and multiple system atrophy (MSA) and from control cases. In the controls, a system-dependent variation in perikaryal Ta-51 immunoreactivity was observed. Very few ventral horn cells and ILC neurons were stained with Ta-51, while large population of DRG neurons and sympathetic neurons were Ta-51 positive. The incidence of perikaryal immunoreactivity in the ventral horn cells was significantly increased in ALS and MSA. Some ILC neurons in ALS were Ta-51 positive and their incidence was significantly higher than that of the controls. These data suggest that both ILC neurons and ventral horn cells are affected with respect to pNFH metabolism in ALS and MSA. No significant difference was, however, detected in the Ta-51 immunoreactivity of both DRG and sympathetic ganglion neurons in ALS and MSA as compared with the controls.