Bisphenol-A polycarbonate (PC)/poly(methyl methacrylate) (PMMA) blends (PC/PMMA) were prepared by melt mixing with and without a trans-esterification catalyst (tetrabutylammoniun tetraphenylborate), which is able to promote inter-exchange reactions between PC and PMMA. Evidences of the ester-ester exchange reaction taking place were pointed out via Fourier Transform Infra-Red and size exclusion chromatography analyses. A series of enthalpy relaxation measurements were carried out for the pure polymers and for blends thereof. The data were analyzed on the basis of the Tool-Narayanaswamy-Moynihan/Kohiraush-Williams-Wafts model. This model characterizes the structural relaxation in the glass transition region by means of four parameters: the apparent activation energy (Delta h*), the nonlinearity (x), the nonexponentiality (beta), and the pre-exponential factor (tau(0)). The apparent activation energy can be determined from the cooling rate dependence of the fictive temperature (T-f) measured using DSC. Delta h* values of homogeneous blend and of the starting polymers were determined in this way, while an estimation of x, beta and tau(0) was proposed. Comparisons were made between a single glass transition temperature PC/PMMA blend and homopolymers data. The experimental values of Delta h* suggest that the degree of cooperativity decreases on going from the starting polymers to the blend.