Photochemical reactions involving the use of singlet-oxygen sensitizers have indicated that singlet-oxygen can cause degradation of cellulose at a rate comparable to that of the hydrogen abstraction mechanism. It has been demonstrated that various dyes active towards the photodegradation of cellulose are also efficient sensitizers of singlet-oxygen, and it is concluded that singlet-oxygen plays a significant role in the degradation of vat-dyed cotton fabrics.