Small-angle neutron scattering and differential scanning calorimetry have been used to probe for changes in the microstructure of nylon fibres following exposure to surfactant, acid and alkali solutions. SANS was also used to investigate fibres that had been subjected to intentional loading environmental exposure, and natural ageing. A number of structural parameters have been derived. The data are capable of differentiating between untreated, treated, loaded, and used fibres. Most] subtle effects are observed. Only exposure to concentrated acid solutions, or applied strain, imparted any significant structural perturbation. These findings, though relevant in a number of areas of application of nylon fibres, are discussed with particular reference to nylon ropes and the laundering of nylon textiles. (c) 2005 Elsevier Ltd. All rights reserved.