Of the many possible isomers of C-78 fullerene, five isomers, thought to be the most stable, have been examined using the semiempirical intermediate neglect of differential overlap INDO/1 and INDO/S models. Two of these structures have C-2v symmetry, two have D-3h symmetry, and one has D-3 symmetry. An equilibrium geometry has been obtained for each of these isomers, and the relative stability has been determined. The electronic spectra have been computed using the INDO/S CI-singles model. The calculated spectra have been analyzed and compared to recent experimentally obtained spectra,(7) confirming that the lowest energy isomers are of C-2v and D-3 symmetry.