The effect of mixing technique and sequence on the distribution of methacrylated-butadienestyrene (MBS) emulsion particles in immiscible blends of polystyrene (PS) and a styrene/acrylonitrile copolymer (SAN) was examined using transmission electron microscopy. The shell of the emulsion particle is essentially poly(methyl methacrylate) (PMMA), which is miscible with SAN but immiscible with PS. In simple thermodynamic terms, the MBS particle should have an affinity for SAN over PS. It was found, however, that the sequence of mixing had a strong influence on the location of the MBS particles. If the PS-SAN interface is established before the addition of the MBS particles, the MBS particles are located exclusively in the SAN phase. If the MBS particles are present at the time the PS-SAN interface is formed, then the particles line up at the interface.