A method for determining cubic response molecular properties of heterogeneously solvated molecules is presented. The molecule is either located at the surface of a metal or solvated alongside the surface of a metal. We represent the metal as a perfect conductor and the solvent as a dielectric medium. The electronic structure of the molecular systems is described both at the uncorrelated and correlated electronic structure levels. The latter is given by the multiconfigurational self-consistent field method. From this method it is possible to calculate fourth order molecular properties such as frequency-dependent second-order hyperpolarizabilities (gamma), three-photon absorptions, two-photon absorption between excited states, and frequency-dependent polarizabilities of excited states. From the frequency-dependent second-order hyperpolarizabilities one can calculate for heterogeneously solvated molecules the third harmonic generation, the static electric field-induced second harmonic generation, the static electric field induced Kerr effect. Calculations of the frequency dependent second-order hyperpolarizability tensor for heterogeneously solvated CO are presented. The calculations show that the second-order hyperpolarizability tensor elements depend strongly on the heterogeneous solvent configuration.