Polarized and depolarized dynamic light scattering have been used to examine the dynamics of concentrated (0.7 < C < 1.0 g/mL) polystyrene solutions in dioctyl phthalate and toluene. Time-temperature superposition of the depolarized intensity correlation functions gave master curves covering more than 10 decades on the time scale. The polarized correlation functions are resolved by different procedures into relaxational and diffusive components having different temperature dependences. When the relaxation rate of the concentration fluctuations approaches the reorientational relaxation rate, the concentration fluctuations become q-independent; i.e., they become rate-determined by the polymer backbone mobility. With a small-molecule solvent such as toluene, however, a part of the concentration fluctuations relaxes faster than the orientational relaxation; i.e., the diffusion occurs in the free volume within the "frozen’ network.