A calorimetric study of binary blends based on recycled, low and high density polyethylene, wastes is presented. The physical properties of these blends were reported previously [1]. A comparison between the first and second differential scanning calorimetry (DSC) traces of blended samples reveals the presence of an intermediate endothermic peak which can be associated to the melting of crystals from mixed molecular species of the single components. Further thermal treatments after the second DSC run at temperatures just below and above the intermediate peak for two compositions (phi(B) = 10 and 30% of high density component) highlight the dependence of the various crystal populations upon annealing. A quantitative analysis of a series of consecutive thermograms for each sample has allowed us an estimation of the relative amount of material associated to the three main endothermic peaks.