A new apparatus to investigate the structure of fluids under Poiseuille shear flow using small‐angle neutron or light scattering techniques is described. Important features of the design include low sample volumes, area average shear rates of up to 5000 s^-1, accurate temperature control over the range of 10–125 °C, and the ability to study the development of flow‐induced alignment phenomena. Small‐angle neutron scattering data are presented for two example systems: the well‐characterized surfactant system C 16 E 6 /D 2 O, used to contrast the effects of Poiseuille and Couette flow, and the block copolymer Synperonic P‐85/D 2 O system. © 1996 American Institute of Physics.