1. Methylcobalamin (Me-B12), adenosylcobalamin (Ado-B12), hydroxocobalamin (OH-B12) and cyanocobalamin (CN-B12) have been estimated by a chromatographic—bioautographic technique in plasma, erythrocytes, leucocytes and bone marrow from normal subjects, hospital controls and patients with untreated pernicious anaemia.

2. Estimates of concentrations of cobalamins have also been obtained in bile, cerebrospinal fluid, liver biopsies and in autopsy samples of liver, kidney, spleen, brain and pituitary.

3. In normal and control subjects, Ado-B12 predominated in all samples except plasma, in which Me-B12 was the predominant form. Me-B12, Ado-B12, OH-B12 and CN-B12 were found in normal erythrocytes, leucocytes and bone marrow and the proportion of each cobalamin was fairly similar in all these tissues. In liver, kidney, spleen, brain and pituitary, the proportions of the cobalamins were more variable. No CN-B12 was detected in these organs.

4. In untreated pernicious anaemia, Me-B12 was disproportionately reduced in plasma, but not in erythrocytes, leucocytes or bone marrow. There was a small increase in the proportion of CN-B12 in plasma, blood cells and bone marrow in untreated pernicious anaemia.

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