In this paper, we study the relaxation behavior of initially amorphous poly(ethylene terephthalate) (PET) films drawn, at 80 degrees C using a draw rate of 2 cm/min, to a draw ratio (lambda) from 1 to 5 and then quenched to room temperature. These films were then heated at different temperatures from 68 to 80 degrees C for different times and their orientation determined. The orientation measurements were performed by transmission infrared spectroscopy and the bands used for the determination of orientation were those at 1340 and 970 cm(-1) for the trans conformers, normalized using the 1410 cm(-1) benzene ring vibration. The crystallinity was determined by thermal analysis. It is shown that when PET is drawn to lambda values up to 2-2.5 (before stress-induced crystallization), the orientation relaxes rapidly at temperatures close to the glass transition temperature of PET. For lambda values of 3 or higher, the orientational relaxation of the amorphous regions is hindered. This effect is ascribed to the development of strain-induced crystallites, which are believed to act as pseudo-crosslinks.