Shear-induced structure formation in solutions of drag-reducing polymers has been studied using several rheo-optical methods including scattering dichroism, turbidity, and small-angle light scattering. Aqueous solutions of high molecular weight partially hydrolyzed polyacrylamide, polyacrylamide, and poly(ethylene oxide) have been examined in the concentration range of 100 to 4000 parts per million by weight. Under high shear flow, increasing turbidity is accompanied by growing lozenge- or butterfly-shaped scattering patterns. With increasing shear, dichroism increases and the orientation angle approaches zero, i.e., scattering centers are aligning with the flow. Fits of the turbidity and structure factor independently demonstrate the presence of micron-sized structures forming under shear flow. (c) 2005 Elsevier B.V. All rights reserved.