The nature of the stress/strain distribution in a highly oriented gel-spun polyethylene under stress has been examined using several techniques. X-ray diffraction has been used to characterize the crystalline strain; these results are compared with the macroscopic stress and strain and with the frequency of the 1060 cm(-1) Raman band. It is shown that the Raman measurements effectively monitor the response of the crystallites and that any sensitivity to taut tie molecules is only a possible consideration at very high stress. A modified fiber composite model is considered the most suitable for predicting the mechanical behavior. It is also suggested that the reinforcement is provided by the microfibrils, which have the required large aspect ratio. At low applied stress, the buildup of stress along the fibril is very rapid, and consequently there is little evidence of stress/strain inhomogeneity. At high stress, however, strain inhomogeneities, which are dependent on temperature and time, are detectable in the crystalline regions. This behavior is also interpreted using a fiber composite model, and the implications for the stress buildup along the fiber are discussed.