AbstractThis paper deals with the reanalysis of serum lipids from previous studies in which deuterated fatty acids were administered to a single person. Samples were reanalyzed to determine if the deuterated fatty acids were converted to deuterium‐labeled conjugated linoleic acid (CLA, 9c, 11t‐18∶2) or other CLA isomers. We found 11‐trans‐octadecenoate (fed as the triglyceride) was converted (Δ9 desaturase) to CLA, at a CLA enrichment ofca. 30%. The 11‐cis‐octadecenoate isomer was also converted to 9c, 11c‐18∶2, but at <10% the concentration of the 11t‐18∶1 isomer. No evidence (within our limits of detection) for conversion of 10‐cis‐or 10‐trans‐octadecenoate to the 10,12‐CLA isomers (Δ12 desaturase) was found. No evidence for the conversion of 9‐cis, 12‐cis‐octadecadienoate to CLA (via isomerase enzyme) was found. Although these data come from isomerase enzyme) was found. Although these data come from four single human subject studies, data from some 30 similar human studies have convinced us that the existence of a metabolic pathway in one subject may be extrapolated to the normal adult population.