Rheological and rheo‐optical studies on nematic solutions of the rodlike poly (1,4‐phenylene‐2,6‐benzobisthiazole), PBT, are discussed in terms of theoretical predictions based on the use of the Ericksen–Leslie constitutive equation for nematic fluids. The behavior of both aligned and unaligned solutions is discussed. Experiments on the former show that the nematic solutions of PBT do not align in a slow shear flow, and that reorientation of the director in a magnetic field is coupled with local flow, producing a phase grating. The grating, which is visualized by its diffraction of light, may also be observed in flow. The textural features of initially unaligned solutions are discussed, and the flow behavior is considered in terms of certain theories based on a polydomain structure in the nematic fluid.