The miscibility of poly(alpha-methylstyrene-co-acrylonitrile) having an acrylonitrile (AN) content of 32 wt % (MSAN-32) with poly(styrene-co-acrylonitrile)s (SANs) was studied by differential scanning calorimeter. To decide the phase diagrams, very long isothermal annealing (sometimes above 200 h) was required. It was found that MSAN-32 is miscible with SAN having AN contents between 28 and 40 wt % at 130 degrees C. The miscibility range is in good agreement with that predicted using a non-hydrogen-bonding solubility parameter approach. Three segmental interaction parameters were calculated from the boundaries separating domains of miscibility and immiscibility. Lower critical solution temperature (LCST) type phase diagrams were found for miscible blends above 130 degrees C. This is the first observation of the presence of LCST behavior for MSAN/SAN blends. It was emphasized that the excessively long times are required to reach equilibrium for these blends.