• Lipofuscin has been reported to accumulate in abnormal amounts in motor neurons of patients with amyotrophic lateral sclerosis (ALS). Microdensitometry was used to quantitate such lipid masses in spinal motor neurons in normal subjects compared with spinal motor neurons in ALS cases. No overall difference in lipofuscin level was found between the normal and the ALS material. Some neurons of intermediate size did show increased amounts of lipofuscin, which is attributed to shrinkage during degeneration by larger cells having proportionately more lipofuscin originally.