1. Whole-body counting has been used to monitor the clearance of [57Co]cyanocobalamin in normal subjects, vegans and patients with pernicious anaemia. After oral administration of 57Colabelled cyanocobalamin (1 μg/l μCi), subjects were counted for radioactivity monthly for a maximum period of 1 year.
2. The results obtained were consistent with a monoexponential clearance model and a least-squares fit showed that there was no significant difference between the mean clearance rates for the vegans and normal subjects.
3. The patients with pernicious anaemia cleared the vitamin significantly more quickly than the normal control subjects.
4. This may be due to failure to reabsorb biliary vitamin B12 in pernicious anaemia because of the absence of intrinsic factor.