The electronic structure of highly-oriented poly(p-phenylenevinylene) (PPV) and unoriented poly(2,5-thienylenevinylene) (PTV) were investigated by high-resolution electron energy-loss spectroscopy (EELS). Performing a Kramers-Krönig analysis, the momentum-dependent dielectric functions could be derived. For the oriented PPV samples, the dielectric functions parallel and perpendicular to the chain axis were determined. In order to study the influence of the vinylene linkages on the electronic properties of these materials, the results were compared with previous measurements on polyparaphenylene (PPP) and polythiophene (PT). © 1991.