This report concerns the study of synaptophysin (SP) expression in the anterior horn of three cases of lower motor neuron disease (L-MND). All patients studied had anterior horn cell degeneration without neuropathological evidence of corticospinal tract degeneration. Spinal cords from six patients with no neurological disease served as controls. Immunocytochemical techniques were used. The results show that in L-MND there is decreased SP immunoreactivity of the anterior horn neuropil, but preservation of immunoreactive dots around the cell body and proximal processes, and the presence of some residual neurons in the affected gray matter that are surrounded by a dense accumulation of immunoreaction products. These findings resemble those of classical amyotrophic lateral sclerosis (ALS), indicating similarities in the distribution patterns of presynaptic terminals in the anterior horn of L-MND and classical ALS.