Tail biting is a widespread adverse behaviour that occurs in growing pigs but, as of yet, no one knows what initially encourages the development of this behavioural problem. It has been suggested that tail biting is linked to a behavioural predisposition, exacerbated by environmental inadequacy, or a nutritional deficiency such as inadequate protein or minerals. Using a model tail test, Fraser (1987, 1991) demonstrated an experimental link between mineral or protein dietary deficiencies and an increased attraction to blood. Using this test, Fraser demonstrated that large individual variation exists between pigs in the extent of their attraction to blood. The current experiment extended this tail test to investigate the nature of the attraction to blood, and to examine factors that may be related to tail biting predisposition.