The application of X-ray photoelectron spectroscopy to the study of the surface chemistry of wool fibres clarifies some aspects of the role of the cystine disulphide bond. The sensitivity of the electron-binding energy of the S(2p) orbitals to the sulphur oxidation state provides information about the extent of surface modification following two different oxidizing treatments using (a) dichloroisocyanuric acid, and (b) hypochlorous acid ('Kroy' chlorination). Interaction of a wool surface with a polymer, Hercosett 125, which is the basis of a shrink-resistant treatment, shows that complete coverage of the wool-fibre surface does not occur even though the average thickness of the polymer overlay is about 1000 (100nm).