The dynamics of an individual chain in a binary polymer blend is investigated. A generalized Rouse equation takes into account the coupling to the dynamics of the surrounding polymer matrix. This generalizes Schweizer’s approach to a multicomponent polymer system. The results are applied to a symmetric binary blend. Emphasis is laid on the role of composition fluctuations, which are strongly enhanced close to the phase separation and then show critical slowing down. This has an impact on the dynamics of individual chains. As a result of the treatment, the internal chain motion is expected to be more strongly affected than the center-of-mass motion. A physical interpretation is presented such that the chains are strongly expelled from unfavorable environments. It is discussed how the results are modified if-instead of a mean-field treatment-the theory of critical phenomena is applied to describe composition fluctuations.