The problem of adsorption of alkali ions on gold is studied from the theoretical point of view. The interactions of five ions, Li+, Na+, K+, Rb+ and Cs+ with the Au atom and the AU(12) cluster modelling the Au(100) surface, were calculated using one of the density functional techniques, namely the B3LYP method. For the 12-atom cluster, an interaction energy and a charge on the ion at its optimal distance from the Au(100) crystallographic plane were computed at three main positions of the ion on the metal surface: hollow, bridge and top. The adsorption energy was found to increase in the order Cs+ < Rb+ < K+ < Na+ < Li+ This same trend is observed in the electron transfer from the metal to the ions. A less clear tendency is found in the adsorption energies of the same ion at the different sites on the surface. For the two smaller ions the hollow site is found to be preferred for adsorption, while for the three larger cations the top position is favoured. For all ions the energy difference between the most and the least stable site on the surface is relatively small (< 10 kJ mol(-1)). The importance of the inner charge distribution inside the metal cluster is also discussed. The artificial interactions between the ions and charges located on atoms in the Au,, cluster were estimated using a simplified model. They are shown to constitute a relatively large contribution to the energy values obtained from the cluster model calculations. A strong dependence of some results on the basis set used for the Au atom is documented.