The hydrogenation of microcrystalline raw paraffin from the dewaxing of heavy neutral oil over Ni-Mo/Al2O3 and Ni-W/Al2O3 catalysts was studied at the pilot plant scale. The diameter and pore structure of the catalyst showed a noticeable influence on the properties of treated paraffins. The use of catalysts with a particle size of 1.5-2.5 mm allowed us to reduce the severity of the reaction conditions. To obtain treated paraffins with acceptable Saybolt color values, temperatures of >310degreesC and pressures of >60 kg/cm(2) were needed. High temperatures resulted in cracking reactions and high oil content, which can be prevented by high hydrogen pressure. The Ni-W catalyst showed higher activity and selectivity than Ni-Mo catalysts. Saybolt color values of >+30 and oil contents of <0.5 wt % can be obtained with Ni-Mo catalysts at 350 degreesC and 60 kg/cm(2), whereas a temperature of 330 degreesC and pressure of 60 kg/cm(2) are required for equivalent results with Ni-W catalysts.