In situ reduction of gold ions, by a strong reducing agent facilitates the formation of gold nanoparticles on suitable metal oxide supports in such a way that a narrower size distribution and smaller particle size are obtained. Improved catalytic activity is also observed. Introducing zinc oxide to titanium oxide causes a surface modification of the titanium oxide and leads to a reduced catalytic activity for CO oxidation. (C) 2003 Elsevier B.V. All rights reserved.