SummarySheep infested by single species of the ectoparasitesDamalinia ovis(biting louse)Psorergates ovis(itch mite) andDemodex canisvar.ovis(follicle mite) exhibit distinctive behavioural symptoms of fleece derangement. Louse infestation may involve intense irritation with rubbing against solid objects and scratching the neck with the hind leg. The irritation of sheep infested by the itch mite is mild—characteristic behaviour, rarely seen, being to bite the fleece in regions easily accessible to the mouth. Follicle mite infestation is usually symptomless. The dermatohistopathology typical of each parasitic infestation is briefly describe