Com. Ni catalyst used for hydrogenation of PhH to cyclohexane under industrial conditions was monitored for several years to det. the decrease of its catalytic activity the bed length along. The results were compared with model calcns. performed under assumption that the only reason for the catalyst poisoning was the action of S compds. The actual redn. of the catalyst activity was lower than the calcd. one because of formation of C deposits on the catalyst surface.