AN abnormal wool, more apparent on older sheep and known as ‘doggy’ wool, is a cause of considerable financial loss in some Merino and Polwarth flocks. Such wool is frequently lustrous and is characterized by reduced frequency of crimps, so that in extreme cases the fibres are almost straight and hair-like. Preliminary evidence is presented here that doggy wool is associated with hyperplasia and cyst formation of the outer root-sheaths of a considerable proportion of the follicle population of affected sheep.