The absortion of vitamin B12 was studied in 9 cases of subacute combined degeneration of the spinal cord before and after the administration of intravenous ACTH in a therapeutic scheme lasting from 19 to 43 days. In 7 cases an increase of absorption was evidenced. The mean difference of change in the urinary excretion test of radioactive vitamin B12 was near the limit of significance. This finding reinforces the indication of the use of corticotropin in subacute combined degeneration of the spinal cord, since the hormone will act both on the allergic component of the demyelinating process and on the deficiency of vitamin B12 absorption. Though the material here analyzed is too small to.warrant a definite conclusion, our results suggest that ACTH influences the vitamin B12 absorption through the intestinal wall, and not by means of an increase of intrinsic factor secretion or a mobilization of vitamin B12 stores.