The sulfur uptake of commercial and laboratory prepared catalysts of the type MoO3¿-Al2O3, CoO¿-Al2O3 and CoOMoO3¿-Al2O3 was studied at 400 °C using H2/SH2 and thiophene/H2 as sulfiding gases. The temperature, time, and H2S partial pressure of sulfiding were varied, and the fraction of sulfur removable by H2 reduction at 400 °C was determined. The influence of the sulfur content on the activity for hydrodesulfurization of thiophene was also measured. Based on these findings the formation of MoS2 and Co9S8 as a result of the sulfidation is considered to be the most likely process, although the presence of small amounts of other sulfurcontaining species cannot be excluded. Experimental evidence is reported for the diffusion of Co2+ ions from the bulk towards the surface of the ¿-Al2O3 support during the sulfiding process. The hydrogenolysis activity was found to decrease with increasing sulfur content for the MoO3¿-Al2O3 catalyst, while on CoOMoO3¿-Al2O3 the reverse effect was observed.