The farrowing crate is one of the most confining forms of animal accommodation found in intensive animal rearing systems and so is subject to criticism from welfare lobby groups. To determine how the welfare of the sow might be affected by the crate, we need to gain an understanding of pre-farrowing behaviour, and the factors that affect its expression. Free-ranging domestic sows will leave the herd on the day before farrowing and walk up to 6.5 km, build a nest and farrow in it (Jensen, 1986). Crated sows are known to become very restless in the day or so before farrowing, and as farrowing approaches they bite at the crate and paw and root at the floor and fittings (e.g. Jones, 1966). It is possible that this behaviour is an expression of the motivation to perform locomotion and nest-building as shown by sows in the wild. To investigate this, three experiments were designed to investigate pre-farrowing behaviour in domestic sows and the influence of straw (a nest-building substrate) on its expression.