DFT calculations have been performed to study the interaction of small gold clusters, Au-1-Au-13, with H and CO. An odd-even oscillation of the H chemisorption energy was observed, with H adsorption onto odd-numbered clusters being more favourable. This correlates with the smaller HOMO-LUMO gaps for these clusters. For CO chemisorption, the overlap between CO orbitals and cluster frontier orbitals is important. As a result, there is no simple relationship between CO chemisorption energy and the frontier orbital energies of Au(n)clusters. (C) 2004 Elsevier B.V. All rights reserved.