Steady shear rheology of entangled polystyrene (PS)-diethyl phthalate (DEP) solutions are investigated using mechanical rheometry and optical birefringence measurements. Polymer solutions are formulated using narrow molecular weight distribution polymers that cover a broad range of molecular weights (3.8×106⩽Mw⩽20.06×106 g/mol) and concentrations of 0.025⩽φ⩽0.26. In polymer systems with N/Ne > 12, cone-and-plate and narrow-gap parallel plate shear flow measurements reveal an unusual transition to non-Newtonian behavior at Wi≪1. The transition is evidenced by early power law η∼γ−β (β=0.45±0.15) deviations from Newtonian fluid response, and is consistent with earlier observations reported by Bercea et al. [Macromolecules 26, 7095–7096 (1993)] and by Islam and Archer [J. Polym. Sci., Part B: Polym. Phys. 39, 2275–2289 (2001)] for solutions of ultrahigh molecular weight polymers in good solvents. The power-law flow regime extends well beyond Wi=1 for most systems studied and its breadth is proportional to th...