The steady state rheological behavior of three narrow molecular weight distribution styrene-isoprene-styrene (SIS) triblock copolymers with different molecular weights and polystyrene (PS) contents was investigated by means of a capillary rheometer using the roundhole and slit die geometry. A monodisperse polyisoprene was also investigated to allow a comparison with the flow behavior of the pure elastomer. Like polyisoprene, all the copolymers exhibit spurt marked by a plateau of the shear stress versus flow rate curve and by a discontinuity of the entrance pressure when a critical shear rate is reached. Near the glass transition of the PS domains, the flow curve is mainly influenced by the PS content and exhibits, with increasing flow rate, first yield stress, and then spurt. On the contrary, at higher temperatures, yield stress and spurt disappear and the theological behavior is qualitatively driven by the overall molecular weight as for linear polymer melts. The values of the critical stress for spurt are significantly larger than that of the polyisoprene matrix and the influence of the PS content on asp., and the sequence of melt flow distorsions were discussed. (c) 2006 The Society of Rheology.