A considerable amount is now known about the endocrine and neuro-endocrine control of parturition. Far less is understood however about the effect of events which may be considered stressful on the parturition process, despite its broad relevance to animal welfare and farm animal production. There is evidence that stress can have highly disruptive effects during parturition. For example, it has been suggested, that in pigs the behaviourally restricting farrowing crates used in commercial farming practice give rise to increased inter-piglet birth intervals and piglet mortality (Vestergaard and Hansen, 1984). Recent work on rodents has suggested that inhibtion of oxytocin secretion mediated by endogenous opioids, might be responsible for prolonged parturition following an acute stress such as a mid-partum change of environment. The aim of the present work was to extend the study of the effects of stress at parturition to a large animal model. We report two studies on the effects on parturition and oxytocin secretion of movement in mid-parturition to a novel environment (environmental disturbance). In Experiment 1 the effect of this disturbance on inter-piglet interval was investigated. In Experiment 2 a fuller investigation was made of the effects of environmental disturbance on a range of measures including inter-birth interval, behaviour of the sow and plasma oxytocin and Cortisol levels. The role of opioids was investigated in both experiments by administration of the opioid antagonist naloxone.