AbstractCorrinoids from various ovine tissue samples (liver, blood, small intestinal fluid and faeces) were analysed using a combination of high‐performance liquid chromatography (HPLC) and a radioisotope dilution assay (RIDA) to estimate the distribution of corrinoids—the cobalamins hydroxocobalamin (OH‐cbl), methylcobalamin (me‐cbl) and 5′‐deoxyadenosylcobalamin (ado‐cbl), and cobalamin analogues—in these tissues. Samples were taken from either cobalt‐deficient or cobalt‐replete ewes, and ruminant and pre‐ruminant lambs. In liver, ado‐cbl predominated, followed by analogues, OH‐cbl and me‐cbl. Supplementation with either cobalt (ruminant) or vitamin B12 injections (pre‐ruminant) increased the amount of ado‐cbl and decreased analogues. In blood, OH‐cbl predominated, followed by ado‐cbl, analogues and me‐cbl, respectively. In small intestinal fluid, the distribution from largest to smallest percentage was analogues, ado‐cbl, OH‐cbl and me‐cbl. In faeces, analogues constituted the greatest proportion, followed by OH‐cbl, ado‐cbl and me‐cbl, respectively. Owing to the small sample sizes only cautionary interpretations can be made. In contrast to humans, where me‐cbl constitutes the highest proportion of corrinoids in plasma and ado‐cbl in the liver, in sheep the amount of ado‐cbl was consistently higher than me‐cbl in all tissues. This may be due to the higher metabolic need of sheep for ado‐cbl due to gluconeogenesis. Analogues and OH‐cbl were found in each tissue, contrary to previous postulations. The much higher amount of vitamin B12 in small intestinal fluid compared with faeces indicates that a large proportion of the vitamin is absorbed by the gastro‐intestinal tract. Copyright © 2005 John Wiley & Sons, Ltd.