Diffusion constant in a random system near resonance

We propose a modification of the traditional Boltzmann equation when scatterers are near resonance conditions. On the basis of this modified equation we find that the diffusion constant is largely renormalized. Our calculated results agree with the recent experimental results of van Albada et al. [Phys. Rev. Lett. 66, 3132 (1991)] for the diffusion of optical waves.