The lumbar cords from 3 cases of familial amyotrophic lateral sclerosis (fALS), one case of vincristine neuropathy, and two control cases were examined with an antiserum to calcitonin gene-related peptide (CGRP). The anti-CGRP intensely labelled the spinal posterior horns in all cases. In the anterior horns, several perikarya and cord-like neuritic swellings, mostly axons, were labelled with the antibody in the fALS cases, whereas CGRP-positive structures were extremely rare in the cases other than fALS. It is possible that the accumulation of CGRP in the proximal axonal swellings and perikarya may result from entrapment of CGRP during the anterograde axonal transport, causing loss of, or decrease in, CGRP at the neuromuscular junction and producing weakness and atrophy of the muscles.