Vitamin B12 absorption, as determined by the urinary-excretion test o Schilling, is reported in 6 patients who have undergone distal ileal bypas surgery. The operation was performed to lower circulating cholestero levels in patients with hypercholesteremia and arteriosclerosis. The bowel in each case was normal. The Schilling-test results were all significantly below the accepted normal limit; they ranged from 4.7 to below 1%. These clinical findings support the data indicating that the ileum is the primary site of vitamin B12 absorption.