Gel-spun polyethylene fibers were analyzed at room temperature with C-13 NMR, using both, CP-MAS and BILEV (Bloch-decay with two-level decoupling). The analysis shows the existence of three different components in the fiber sample-a crystal component, an amorphous component and a third component, named the oriented, mobile component. This latter component has a C-13 chemical shift that is similar to the crystalline chemical shift, but with a mobility, expressed by T-1, that is closer to the amorphous component. The chemical shift and T-1 are as follows : 34.06 ppm and 28.1 s for the crystalline part; 31.70 ppm and 0.3 s for the amorphous part; and 34.06 ppm and 1.8 a for the oriented mobile component. The percentages are 63.2% crystalline; 34.0% oriented mobile, and 2.8% amorphous component. Using proton spin-diffusion measurements, it was possible to estimate the domain size of the crystalline and oriented mobile components to be 62.8 and 13.2 nm, respectively, in agreement with the results of a full-pattern x-ray study on the same sample. After melting of the fiber at 450 K and recrystallization on cooling, the oriented, mobile component is dramatically reduced.