Blends composed of poly (ethylene terephthalate) and a polyarylate have been melt-mixed and molded in a reciprocating screw injection-molding machine for different plasticization times. Interchange reactions between the blend components occur during processing and at a greater level as the plasticization time increases. These reactions led to a progressive homogenization of the blends as well as to a hindered crystallization of PET. The effect of the plasticization time on the mechanical properties of the blends seems to be a consequence of interchange reactions as well as of the degradation of the blends at the highest plasticization times.