Confocal Raman microscopy (CRM) has been used to extract dye diffusion data from poly(ethylene terephthalate) (PET) fibres dyed with Disperse Yellow 23 under supercritical CO2 conditions. Spectral information as a function of depth was measured in a non-destructive manner using dry and oil objectives in confocal Raman mode. Mapping along the radius of the fibre cross-section was performed and compared to the data from the confocal measurements. A significant dye concentration gradient has been observed along the line normal to the fibre surface which the data from the oil confocal measurements accurately describes to a depth of 45 mu m. The effect of the supercritical CO2 dyeing process on the fibre morphology has also been evaluated using CRM. (c) 2005 Elsevier Ltd. All rights reserved.