The activity of titania based copper and platinum monolithic catalysts in the reduction of nitrogen oxides was studied with exhaust gases from a Diesel engine injecting fuel as reductant. Combining both catalysts, a two-stage system was designed, studying the influence of the copper catalysts composition on its performance with synthetic gas mixtures. The influence of reactants concentration and operating conditions was also investigated. Taking into account these results, a double-bed system with a cell density of 33 cell cm(-2) (210 c.p.s.i.) was prepared. Linear velocity had a strong influence on the performance of the Pt catalyst and of the double-bed. Two NOx conversion maxima were observed with Pt/TiO2 at 225 degrees C and 350 degrees C operating at 6.6 m s(-1). Promising NOx conversions were achieved in the temperature range 200-450 degrees C.