The mixed crystal i.r. technique has been applied to polyethylene single crystal mats after rolling at room temperature to roll ratios up to 6.0. Reduction in the absorbance of the outer CD2 bending components provides evidence of lamellar breakup. Model calculations indicate that the size of blocks which break away from the crystals is reduced to approximately 36 angstrom for a ratio of 6, while X-ray diffraction data show that crystallite reorientation occurs progressively with increasing roll ratio. Changes in small-angle X-ray scattering and the Raman longitudinal acoustic mode with rolling demonstrate that crystallite stacking periodicity is gradually lost and that crystal thickness remains unchanged.