The first step in the two-step CO-catalyzed conversion of H2S to H-2 and sulfur, reactions 1 and 2, has been studied in order to establish the optimal experimental conditions for the reaction. Without a catalyst, H2S conversions of the order of only 1-2% could be achieved. NiS on alumina proved to be an efficient catalyst, and at 267 degrees C, H2S conversions reached 52% or 100% of the thermodynamic limit. Small amounts of CO2 and CS2 have also been detected among the products. In comparative experiments using CoS on alumina as the catalyst, up to 67% conversion, representing 100% of the thermodynamic equilibrium H-2 yield, could be achieved at a substantially lower temperature, 177 degrees C. Furthermore, formation of CO2 and CS2 was found to be negligible (<1%) at this low temperature, eliminating the need for the suppression of the COS disproportionation reaction.