The glass transition and the effect of specific interactions on this transition process in a binary polymer blend of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN), which have very similar glass transition temperatures, have been investigated by means of modulated differential scanning calorimetry. The blends investigated were miscible blends of PMMA and SAN and a physical mixture of the two constituent polymers. Using the differential of heat capacity versus temperature signal, the technique has been shown to be able to resolve the two glass transitions so long as their difference is not less than about 5 degrees C. The value of heat capacity of the miscible blend does not satisfy simple linear addition of the heat capacities of the two component polymers over the glass transition region. It is believed that this enhancement of heat capacity in the glass transition region results from specific interactions between segments of the two polymers.