The miscibility in blends of poly(methyl methacrylate) (PMMA) with poly(styrene-co-methacrylonitrile) (SMAN) was examined by solid-state NMR and fluorescence spectroscopy. The value of the excimer/monomer fluorescence intensity (I(E)/I(M)) in the blends provides a sensitive measure of phase separation. A miscibility window in the blends of PMMA and SMAN containing about 30-65 mol % methacrylonitrile (MAN) monomer has been observed by fluorescence experiments. Measurements of T1pH by solid-state NMR have shown that blends containing 50:50 wt % PMMA blended with each of polystyrene, poly(methacrylonitrile), SMAN (MAN : 18.9 mol %), and SMAN (MAN : 87.6 mol %) are phase-separated. There is an intermolecular penetration between PMMA and copolymers in the blends of PMMA with SMAN (MAN : 43.8 mol %) and SMAN (MAN : 70.9 mol %) at a level of less than about 6 nm. However, the fluorescence data would indicate that intimate mixing does occur below this level. An analysis of the T1pH values for SMAN has indicated that the sequence distribution has an important effect on the interactions in the copolymer system.