Drag-reducing surfactant solutions are very sensitive to shear. Shear can induce nanostructural transitions which affect drag reduction effectiveness and rheological properties. Literature reports on the effects of shear on different micellar solutions are inconsistent. In this paper, the effects of shear on three cationic drag-reducing surfactant solutions each with very different nanostructures and rheological behaviors, Arquad 16-50/sodium salicylate (NaSal) (5 mM/5 mM) (has thread-like micelles, shear-induced structure and large first normal stress (N-1)), Arquad S-50/NaSal (5 mM/12.5 mM) (has branched micelles, no shear-induced structure and first normal stress is about zero) and Arquad 16-50/sodium 3,4-dimethyl-benzoate (5 mM/5 mM) (has vesicles and thread-like micelles, shear-induced structure and high first normal stress (N-1)) are studied by small-angle neutron scattering (SANS), together with their theological properties, drag reduction behavior and nanostructures by cryogenic-temperature transmission electron microscopy(cryo-TEM). The differences in the theological behavior and the SANS data of the solutions are explained by the different responses of the nanostructures to shear based on a two-step response to shear. (C) 2009 Elsevier Inc. All rights reserved.