Rayleigh scattering studies were conducted in order to examine the elongational flow-induced crystallization behaviour of poly(ethylene terephthalate) (PET) in the supercooled liquid state (100-130 degrees C). In the specimen elongated at 110 degrees C where spherulite growth was negligible, initially nothing happened, but flow-induced crystallization then occurred rather suddenly at a critical tensile strain of epsilon(=(epsilon) over dot(0)t) approximate to 2 in Hencky units, independent of the strain rate (epsilon) over dot(0). At this temperature the H-v (cross-polarized) scattering yielded two-point patterns parallel to the elongational direction with strong streaks in the perpendicular direction. The result implies that molecular orientation proceeded along the flow direction and the crystalline domain grew transverse to the oriented chains. In contrast, at 130 degrees C, especially with low (epsilon) over dot(0), where spherulite growth was rapid, a four-leaf-clover pattern typical of spherulites was observed at the start of elongation epsilon = 0. In the following stages, spherulite growth surpassed the destruction of existing spherulites and/or flow-induced oriented crystallite formation, and a smeared four-leaf-clover pattern was thus observed even at a level of epsilon = 1.3. (C) 1997 Elsevier Science Ltd.