Catalysts used for selective catalytic reduction of NOx on diesel engines were deactivated for 890 and 2299 h in the exhausts from a diesel engine running on Swedish diesel fuel mark 1. The deactivated catalytic monoliths (100 mm long) were cut in 10 mm pieces along their axis and were characterized by physicochemical methods as well as by determination of the activity in the reduction of NOx by NH3 and in the oxidation of NH3 by O-2.