Treatment of polyethylene terephthalate fibres with hydrolase preparations from Thermomonospora (Thermobifida) fusca and Fusarium solani f. sp. pisi resulted in an increase of the hydrophilicity of the fibres determined by measurement of their dyeing behaviour with reactive dyes and their water absorption ability. Reflectance spectrometry of treated fibres dyed with a reactive dye showed that the colour became more intense corresponding to an increase of hydroxyl groups on the fibre surfaces and indicated a stepwise peeling of the fibres by the enzymes comparable to the effects obtained by alkaline treatments. The synthetic fibres treated with the hydrolase from T. fusca also showed enhanced water absorption ability further confirming the increased surface hydrophilicity caused by the enzyme.