Resonant Raman scattering of excitonic polaritons at LO phonons in ZnCdSe/ZnSSe superlattices at room temperature reveals strong spatial dispersion effects near the transverse excitonic resonance frequency . For incident photon energies below , the LO phonon anti-Stokes frequency shifts exceed the Stokes shifts, while the inverse relation holds above . All experimental results can be well described in the excitonic polariton formalism in terms of exciton branches with positive and negative excitonic masses above and below , respectively, and an additional damping parameter.