Incoherent inelastic neutron scattering experiments were performed on highly drawn fiber of nylon 6. The sample was about 47% crystalline in the thermodynamically most stable a form. The spectra were measured in the 35-125 meV range with a filter-analyzer spectrometer using a Be-graphite low-pass Bragg cutoff filter. By employing two scattering geometries, we were able to discriminate between vibrational modes with hydrogen displacements along polymer chains from modes perpendicular to chains. In the low-frequency range we have observed exclusively parallel modes at 45, 54, and 65 meV due to polymer skeleton deformations. CH2 rocking and twisting vibrations and some of the amide modes are also observed, and their polarization is discussed. A preliminary vibrational analysis of a single polymer chain using force constants calculated by the semiempirical Hartree-Fock AM1 method has been performed, and the calculated and measured spectra are compared. Overall, a good agreement between the neutron scattering spectra, the AM1 calculation, and IR and Raman data is found.