In this paper, investigations on the morphology development under uniaxial extensional flow are reported for an immiscible [poly(styrene-co-acrylonitrile)/polypropylene] and a partially miscible [poly(styrene-co-acrylonitrile)/polycarbonate] blend. Creep experiments were performed on samples with various initial droplet sizes under different constant stresses using an oilbath rheometer. At the end of each experiment, the samples were quickly removed from the rheometer and quenched in liquid nitrogen to freeze in the morphology. By means of scanning electron microscopy, their morphologies were visualized and the accordance with the critical capillary number was analyzed. A satisfactory agreement was found for the immiscible blend. In contrast, the partially miscible blends exhibited much smaller droplet deformation than expected and no fibril formation was found for any set of the parameters applied. (C) 2010 The Society of Rheology. [DOI: 10.1122/1.3380856]