Comparative and comprehensive studies of poly(styrene-co-acrylonitrile) (SAN) and poly(vinyl chloride-co-vinyl acetate) (VYHH) blends using several blending techniques such as melt-mixing, solution blending and co-precipitation methods by an appropriate non-solvent were performed. The compatibility of the blends was studied by measuring the glass-transition temperatures (Tgs) of the blends and also by measuring the heat capactiy change (ΔCp) at the glass transition temperature for each blend using differential scanning calorimetry (DSC). The presence of either one or two Tgs has been used as a criterion to determine the miscibility of each blend over a range of composition. It was found that for miscible blends the heat-capacity changes are equal to the calculated values, but for immiscible blends the experimental ΔCp is smaller than the calculated value. The results varied significantly from one blending technique to another and from solvent to solvent. Copyright © 1996 Elsevier Science Ltd All rights reserved.