The effects of pressure and temperature on the rheological properties of poly(ethylene oxide) (PEO) aqueous solutions, with and without added inorganic salts, are reported. A slight decrease of the viscosity at low temperatures and an increase of the viscosity at high temperatures with increasing pressure were noted. However, the most striking effect was the lowering of the phase separation temperature with increasing pressure, which manifested itself in large changes in the viscosity of the solutions. This effect is proposed to be due to the lowering of the solvent quality of the water for PEO, brought about by the disruption of the hydrogen bonding in the water which occurs on increasing the pressure.