Drop breakup is an important part of the study of polymer blending. During mixing, large domains of fluids are stretched and broken up into smaller droplets. To obtain a good dispersion of a multiphase system, the size and location of the suspended phase domains need to be optimized. It was seen that breakup mechanisms depend on the deformation process and the material studied. Shear and extensional flows were investigated and different breakup phenomena were observed. A Newtonian fluid and a viscoelastic solution for the dispersed phase were used to focus on the differences due to the fluid properties; the matrix fluid was Newtonian. (C) 2000 John Wiley & Sons, Inc.