The metabolic fate of rumenic acid (9cis,11trans-octadecenoic acid) related to its position on the glycerol moiety has not yet been studied. In the present work, synthetic triacylglycerols (TAG) esterified with oleic and rumenic acids were prepared. Rats were force-fed synthetic dioleyl monorumenyl glycerol with (14)C labeled rumenic acid in the internal (sn-2) or in the external position (sn-1 or sn-3). Rats were then placed in metabolic cages for 16 h. At the end of the experiment, the radioactivity in tissues, carcass and expired CO(2) was measured. Rumenic acid that was esterified at the external positions on the TAG was better absorbed and oxidized to a greater extent than when esterified at the internal position. The fatty acid from the 2-TAG form was also better incorporated into the rat carcass. In the liver, rumenic acid appeared mainly in TAG (50%) and to a lesser extent in phospholipids (33%) whatever its dietary form. Moreover, analyses of lipids from Camembert cheese and butter revealed that rumenic acid was located mainly on the sn-1 or sn-3 positions (74%). Taken together, these data suggest that rumenic acid from dairy fat may be well absorbed and used extensively for energy production.