The absorption of labeled vitamin B12 in 29 cases of subacute combined degeneration of the spinal cord was studied. The diagnosis was based on the classical neurologic picture and on the presence of gastric achlorhydria and eventual blood or bone marrow changes. The neurologic manifestations were evaluated in a semiquantitative way and were correlated to the results of the urinary excretion test of vitamin B12. The absorption of vitamin B12 was not significantly correlated to the neurologic picture as a whole, or to the peripheral and dorsal funiculi syndromes. However, a significant negative correlation was found between the pyramidal syndrome and the absorption of vitamin B12. The results are confronted with the significance of vitamin B12 in the synthesis of myelin sheaths and ribonucleic acid, the essential role of RNA for the life of the nerve cells and the long axons being emphasized.