The activities of MoO3-Al2O3 catalysts promoted with various amts. of Co, Ni, Zn, and Mn were detd. in pulse and continuous flow expts. for the hydrodesulphurization of thiophene at atm. pressure and 400 Deg. The initial activities of a MoO3-Al2O3 and a CoO-MoO3-Al2O3 catalyst as inferred from pulse expts. are equal. Continuous flow expts. for all catalysts show that the activity decays rapidly and approaches a steady-state level that depends on the promoter and its concn. Max. steady-state activity levels are attained for each of the promoter ions at different metal-to-Mo ratios. Some models are discussed in an attempt to explain the exptl. results. A preliminary investigation of hydrogenation activity of the above-mentioned catalysts is reported. With increasing promoter content a min. for the initial hydrogenation activity is found. Hydrocarbon satn. at the steady-state is comparatively insensitive to the nature of the promoter ion, which may be associated with the sulphiding of the surface.