The effect of the presence of steam on the catalytic activity of MgF2 supported binary copper and manganese oxides in the reaction of NO + C3H6 + O-2 has been investigated in comparison to that on the activity of single metal systems such as Cu-O/MgF2 and Mn-O/MgF2. The reaction was performed for different compositions of the reaction mixture, i.e. under reducing, stoichiometric and oxidising conditions. The most resistant to steam proved to be the mixed Cu-Mn-O/MgF2 system, with a high conversion of NO to N-2 . When the inflow of steam was stopped, the catalyst underwent regeneration. (C) 2004 Elsevier B.V. All rights reserved.