Communication: The performance of organic light-emitting diodes based, for example, on poly(p-phenylenevinylene) could be more easily optimized on the basis of a thorough knowledge of the energies of the electron affinities and the ionization potentials of the materials. Here, results from UV-photoelectron spectroscopy are presented which allow the determination of the absolute binding energies of the occupied molecular orbitals of oligo-PPV. These results are compared with values calculated using semiempirical methods.