The pig industry in the UK now faces considerable public disquiet over the types of environments in which modern pigs are kept and the husbandry procedures they are subjected to. In response to this industry and Government have encouraged scientific research into pig welfare to obtain information by which to objectively assess well-being. The aim of this visit was to review current advances in the study of stress, a concept that has long been central to welfare research. A broad range of techniques for measuring stress are reviewed with special reference to the information they yield on the mechanisms and functions of stereotypic behaviour in sows. There is increasing reliance on the experimental analysis of behaviour and on methodologies that allow simultaneous recording of behavioural, physiological and neurological events. There is also greater attention on the adaptation of physiological systems to chronic stress. Recently it has been demonstrated that whilst close confinement of sows does not result in chronically elevated levels of Cortisol or heart rate, it does result in an increased sensitivity of these systems.