Catalysts with Pt, Re and Pt-Re supported on gamma alumina were prepared by impregnation or catalytic reduction methods. The activation was performed by calcination-reduction or only direct reduction treatment. These catalysts and a commercial one were sulfided with H2S at 500 degreesC and characterized by chemical analysis, TPR, test reactions (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), chemisorption of H-2 and O-2 and TEM. The test reactions were affected by S according to the interaction Pt-Re and metallic dispersion of the catalysts, which are functions of the preparation technique. The presence of S inhibits Hz chemisorption, which cannot be used as a measure of the metallic dispersion. Nevertheless, sulfidation or Pt-Re alloying does not affect the O-2 chemisorption and this chemisorption can be used to calculate the total (Pt+Re) metallic dispersion with a stoichiometry ratio Pt or Re/O equal to 1.