[en] The hydrogen isotope exchange of Brefeldin-A with tritium gas (T₂) in 1,4-dioxane was studied over a commercial palladium catalyst supported on diatomaceous earth (5% metallic weight). The effect of the gas phase was studied. Addition of air in the gas phase led to an increase of the catalytic activity. Moreover, exchange was enhanced when the air/T₂ ratio reached a value of 4. This latter result is interpreted, principally, in terms of a strongly poisoning of the metallic particles together with an effect of the T₂ partial pressure. Through the comparison with Pd(II) oxide, the role of the support is also shown. The specific activities ranged up to 2.8 Ci/mMoles. The labelled product was analyzed by ³H NMR. Possible mechanisms for tritium incorporation are discussed and two different adsorbed species, on the catalyst surface, are involved. (author)