A modified polypropylene fiber was prepared containing 6% of a basic polymeric additive. The fiber was drawn to various ratios and its dyeability with an acid dye was tested. Structural changes due to the drawing were evaluated by application of eight different physical techniques: wide-angle X-ray diffraction, small-angle X-ray scattering, dark-field and optical microscopies, scanning electron microscopy, and density, birefringence, and tensile testing. Variations in dyeability were attributed to density variations from macrovoids in the specimen.