Intrinsic deactivation kinetic parameters of a commercial nickel/Kieselguhr catalyst (Ni-0104T) were determined by poisoning of the benzene hydrogenation reaction with 1-propanethiol from 68 to 120 T. Mercaptan concentrations of 75, 79, 115, and 290 ppm were used. The reaction was carried out at initial conversions of below 6% within a bed diluted with glass beads to achieve better temperature control. A procedure to measure the deactivation kinetic parameters based on the cyclohexane molar concentration is described in detail. Poisoning values of. the preexponential factor and activation energy were found to be 1.45 x 10(-4) (Pa.s)(-1) and 3.87 kJ.mol(-1), respectively, and were comparable with integral reactor data and parameters previously found for thiophene poisoning.