A method for crystallizing oriented samples of the gamma-phase of isotactic polypropylene (iPP) under atmospheric pressure in the presence of nucleating fibers has been developed. The technique uses iPP grades of high molecular weight and high isotacticity and produces a mixture of alpha and gamma-phase crystals within the matrix of both pitch-based carbon and Kevlar(R)-reinforced composites. Two-dimensional wide-angle X-ray scattering (WAXS) patterns from these samples show that the content of the gamma-phase decreases as the fiber loading in the composites decreases, suggesting that the gamma-phase is directly nucleated by the fibers.