Biodegradation of textile fibres caused by fungi and bacteria is anything but a rarity. Cellulosic fibres such as cotton, linen and hemp are preferentially attacked by mould fungi, while wool is threatened particularly by bacteria. In all these cases the substance of the fibre itself provides a good culture medium on which the various microorganisms can thrive. But synthetic fibres, too, can be attacked. Here the lubricants and spinning oils consititute the medium on which the microorganisms involved are identified by staining. This, and the causes of degradation due to fungi and bacteria are outlined with reference to a variety of actual case histories.