An approximate self-consistent field method is described for calculating valence shell excitation energies and molecular structures. This uses many of the simplifications of calculations based on the neglect of differential overlap, but is extended by the use of atomic orbital exchange integrals to resolve open-shell configurational degeneracies in all cases (an exchange modified zero differential overlap method, EMZDO). The accuracy of this method is tested by application to CH, OH, CH2, NH2, H2O, NH3and H2CO, with encouraging results in most cases.