The critical dynamics of a low molecular weight binary polymer blend of polystyrene and polyisoprene is studied near the critical point by dynamic light scattering. Fast and slow modes are observed in the polarized mode in accordance with previous experiments in similar low molecular weight binary polymer blend melts. A new mode is detected in the depolarized dynamic light scattering experiment that displays very weak q(2)-dependence. The intensity of the new depolarized mode becomes zero at high temperatures and gains considerable intensity as the critical point is approached.