AbstractThe Lindlar‐catalysed deuteration of methyl stearolate was studied to determine the effect of various poisons on the rate of reaction and on the isotopic purity of the methyl oleate‐9, 10‐d2produced. Poisons containing both exchangable and nonexchangable α protons on the heterocyclic ring [quinoline, quinaldine, γ‐collidine, acridine, and pyridine] were used. All poisons yielded methyl oleate‐9, 10‐d2having 94–97% isotopic purity. Very little over‐reduction of oleate to stearate occurred. Lindlar‐catalysed H‐D exchange involving the poison