The evolution of LAM contours in the Raman spectrum of polyethylene fibers as draw ratio increases is studied. Profiles of the length distribution of straight-chain segments (SCS) have been determined from the spectra. In fibers up to 20 μm thick, bimodal SCS length distribution occurs. A double maximum has also been observed in the spectra of samples prepared from the blend of polyethylenes with molecular weights of 8 × 104and 2 × 106. In one-component polymer the peak of the SCS length distribution function relating to shorter regular sequences is attributed to the contribution of the surface layers enriched by the low-molecular fraction of the molecular mass. This conclusion is confirmed by the results of chain orientation studies carried out by infrared ATR spectroscopy: At a distance of 2–4 μm from the fiber surface, there has been detected a layer with an orientation which is considerably lower than that in the bulk of a sample.