Reaction-diffusion dynamics in complex média is analyzed. The diffusion operator is decomposed into a deterministic and a random part. In the absence of chemical reactions it is shown that randomness enhances the rate of spread of an initial inhomogeneity and reduces the stationary diffusion flux. When chemical reactions are included, an augmented reaaiondiffusion équation is derived, featuring an effective diffusion coefficient that dépends explicitly on the chemical kinetics. The influence of

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... randomness in the onset of chemical instabilities leading to selforganization is discussed.