Blown extruded polyethylene films without stabilizers have been exposed outdoors under severe weathering conditions in the Sahara. The chemical aspect of aging has been followed by IR spectroscopy. The mechanical aspect of aging has been monitored by means of a nondestructive method. It consists of measuring velocities and attenuations of ultrasonic waves propagating in several directions in the film plane. Stiffness constants and energy dissipation terms have been calculated. From the results obtained it is shown that stiffening of the material leads to an increase of velocities and a decrease of wave attenuation. Moreover, the stiffness constants as well as the energy dissipation terms vary with aging and show a changing anisotropic character of the films. (C) 2003 Wiley Periodicals, Inc.