A novel experimental system is developed to study the morphological development of a model immiscible polymer blend system (polyisobutene-polydimethylsiloxane) in complex, transient flows. A simplified analysis technique using small angle light scattering probes the microstructure of the blend in situ and provides information concerning the overall deformation state of the blend. Depending on the viscosity ratio of the blend, the morphological evolution is more strongly influenced by either the transient shear or elongational component of the Row. Steady state modeling is also applied to describe these transient Rows. The models are able to predict the general trends seen in the experimental data including the effect of changing blend viscosity ratio and initial morphology. (C) 2001 The Society of Rhelogy.