An extensive ab initio study of the benzene-Pt and benzene-Pt + complexes is presented. The benzene-Pt complex has been found to have a C s equilibrium structure with Pt bonded to one of the C-C bonds in a bridged position above the plane of benzene, while the cationic complex has a C 6 v structure. Covalent forces lead to the formation of the Pt-benzene molecular complex, while electrostatic interactions prevail in the case of the benzene-Pt + complex. The reaction pathway of Pt + towards benzene has been studied in both the ground and lowest excited states.