Ternary PBT-PC/phenoxy blends were melt mixed for periods of time up to 110 min to determine the development of interchange reactions among the blend components. This development was evaluated by means of solvent extraction and DSC measurements on blends obtained after characteristic blending times shown in the torque vs. blending time curve. PBT reacts, after very short blending times and, probably due to residual catalyst, mainly with phenoxy. Although at high phenoxy contents a single torque peak is observed, at low phenoxy contents two peaks are observed that correspond to the two stages in which the reaction takes place: at the beginning in the phenoxy-rich phase and later in the overall blend.