In a previous paper (Macromolecules, 2005, 38, 9221), the enthalpy of mixing in poly(DL-lactide)/poly(vinyl phenol) blends was directly measured by DSC. The first DSC scan for solution/precipitation blends showed phase separation, but miscibility was observed in the second DSC scan. Hence, miscibility was achieved after thermal treatment, an unusual behavior in polymer blend current research. However, the exothermal event observed during the first heating scan could also be the result of a chemical reaction. In this work, a new research study conducted to elucidate the nature of the exothermal heat observed in PDLA/PVPh during the first DSC heating scan. Since the single-phase PDLLA/PVPh blend obtained after thermal treatment can be redissolved and reprecipitated, results obtained in the consecutive DSC scan prove that the rocess is completely reversible. Furthermore, GPC and C-13 NMR results provide evidence that there is no change in the chemical structure of the studied polymers before and after the thermal treatment, which evidences the absence of transesterifieationreactions. Therefore, it can be concluded that the exothermal heat is the result of a mixing process, and miscibility is a consequence of specific interactions.