Rheo-infrared spectroscopy was used to study the development of orientation of molten narrow molar mass fractions of poly(ethylene oxide) [molar masses between 18,000 and 120,000 g/mol] during non-Newtonian shear flow at shear rates between 2 and 270 s(-1) and temperatures between 75 and 100 degrees C. The steady state degree of orientation [expressed as the Hermans orientation function (f(ss))] reached a saturation level with increasing shear rate; f(ss) increased with increasing molar mass (M) according to f(ss) = C-1 - C-2/M (C-1 and C-2 are coefficients; the latter depended on shear rate and temperature). The coefficient C-1 (f(ss)) for a polymer with infinite molar mass took a universal value close to 0.05 for the temperatures and shear rates used). Under large shear stresses, the relationship between stress send orientation deviated markedly from linearity. The time to establish a steady state level of orientation was proportional to M-1/2. The recovery of the isotropic state after the cessation of shear could initially be described by a simple exponential relaxation law: f proportional to e(-t/tau r), where tau(rho) is the relaxation time. The latter showed a weak molar mass dependence according to tau(Gamma) proportional to M-0.6 sind an Arrhenius temperature dependence with an activation energy of similar to 60 kJ/mol. The relaxation of the shear stress after the cessation of shear was more rapid than the recovery of the isotropic state.