The sulfide catalysts Ni/C, Mo/C, Ni-Mo/C and Ni-Mo/alumina were compared in parallel hydrodesulfurization (HDS) of 3-methylthiophene and hydrodechlorination (HDC) of o-dichlorobenzene in a flow reactor at 1 MPa and 300 degrees C. The work was related to the disposal of chlorinated organic wastes contaminated by sulfur. The magnitude of the synergism in activity between Ni and Mo in the composite Ni-Mo catalyst observed both for HDS and HDC was significantly smaller for HDC than HDS. HDC was faster than HDS over all catalysts studied. The Ni/C sample exhibited the highest selectivity to HDC versus HDS and also surprisingly high HDC activity, which was higher than that of the commercial Ni-Mo/alumina catalyst. It was concluded that HDC and HDS can be uncoupled by changing the active sulfide phase and that significant room exists to develop sulfide HDC catalysts with better activity than the conventional Go-Mo or Ni-Mo/alumina catalysts.