The effects of mech. and thermal treatments on the mol. anisotropy of poly(m-phenyleneisophthalamide) (I) [24938-60-1] and poly(p-phenyleneterephthalamide) (II) [24938-64-5] fibers were detd. by attenuated total reflection spectroscopy using a deuterium exchange method and by wide-angle x-ray diffraction. Amorphous I fibers developed orientation and crystn. when drawn above the glass temp. The diffraction patterns of drawn II show that the scattering intensity of the noncryst. domain is concd. in the vicinity of the equator indicating that the polymer chains in these regions are preferentially aligned in the fiber access direction. The high degree of D exchange in the undrawn I fibers was consistent with the random orientation of polymer chains in a primarily amorphous structure.