Samples of oriented nylon film and filament were treated with anhydrous HCl and examined in the near-infrared region of 9000 to 3700 cm−1with polarized light. The results are in agreement with previous observations made in the 3600–600 cm−1region, and corroborate earlier evidence that HCl interacts with the peptide linkage. The disorienting effect of the HCl is also reflected in the spectrum of the treated specimens.