Copolymers made by ester exchange reaction have been obtained from poly(ethylene terephthalate) (PET)/poly(bis-phenol-A carbonate) (PC) blends during melt mixing. The copolyesters were isolated by thin-layer chromatography (TLC) and identified by infrared spectroscopy. It was found that the quantity of copolymer formed was increased by the temperature and duration of melt mixing. The PET/PC blend was found to react at 270°C within 10 min, as detected by TLC. After 60 min, the pure PC had disappeared. The miscibility of PET/PC blends was found to be markedly aided by the addition of as little as 2% of the copolymer isolated by TLC.