To investigate the possible role of surface sulfur in the activation of dihydrogen, the reaction of D2S with H-2 was carried out at 423 K on a presulfided NiMo-Al2O3 catalyst. The incorporation of D atoms in H-2 shows that the catalyst is capable of dissociating H2S and H-2 into species which by recombination make the exchange of hydrogen atoms possible between these molecules. This can be considered as evidence of the involvement of surface sulfur in the activation of dihydrogen.