Conditioning of nylon-6 by immersion in metal chloride solutions modifies the mode of deformation under an applied tensile stress. Infra-red spectroscopy of salt-treated films shows significant modification of the spectrum, indicating changes in the intermolecular bonding. Modulus measurements support the hypothesis that modification of the intermolecular bonding in nylon results in some chain stiffening. This stiffening of the network of chains reduces the mobility that is required for shear deformation. This in turn leads to the onset of scission crazing. NaCl, however, spectroscopically shows no evidence for nylon-salt interactions having occurred. The deformation behaviour of both thin-film and bulk samples of NaCl-treated nylon-6 reflect the absence of any salt-amide interaction.