Two phases of intestinal excretion are demonstrated after a parenteral dose of (58)Co vitamin B(12). The first phase was maximal immediately after injection, and was related to plasma radioactivity. The second phase was delayed 36 to 48 hours and was related to labelled cells reaching the tips of the villi. The loss of vitamin B(12) through increased exudation and rapid cell exfoliation together with failure of reabsorption may play a part in the deficiency state seen in the coeliac syndrome.