In 10 cases of subacute combined degeneration of the spinal cord the absorption, clearance and utilization of labeled fat was studied. In 4 cases disorders of the lipid metabolism were found. Although not significantly, the peripheral and dorsal funiculi syndromes were more severe in the 4 cases with impaired fat metabolism than in the normal cases, while the pyramidal syndrome was almost the same in the two groups. The whole neurological picture was also more severe in the 4 cases with disorders of fat metabolism. These results seem to indicate that the impairment of lipid metabolism evidenced in such cases bears no direct relationship with the demyelinating process in general, and would rather attend a deficiency of metabolites (probably B-complex vitamins) other than vitamin B12, which play a more significant role in the preservation of the peripheral nerves.