By use of the Springer-Wolfle rheophotometer, the shear-induced orientation of high-molar-mass polystyrene (M(w) = 10.3 x 10(6) g mol(-1)) is investigated in dilute solution. It is known that the degree of molecular orientation in extremely good and poor solvents is significantly different and, furthermore, that its dependence on shear rate is a function of solvent power. For this reason, the present investigation deals with polystyrene in solvents of intermediate quality, represented by binary mixtures of poly(methylvinylether) (PMVE) and toluene. Owing to the variation of the PMVE fraction, which builds an isorefractive pair with toluene, a variation of both solvent quality and viscosity is realized. This investigation proves that the degree of orientation is induced not only by hydrodynamic interaction but also by thermodynamic interaction, and therefore describes a non-linear function of solvent power. The observed dependence of the rheo-optically detected molecular orientation on solution properties is interpreted and discussed in the light of various theoretical predictions.