Because continuous social support during labour is a component of care in many societies but inconsistent in our own, the clinical effect of support during labour on maternal and neonatal morbidity were studied. Social support was provided by female companions. Four hundred and sixty five healthy primigravidous women were enrolled using a randomised design. Compared with 249 women undergoing labour alone 168 women who had supportive female companions throughout labour had significantly fewer perinatal complications (p less than 0.001), including caesarean sections (7% v 17%, p less than 0.01) and oxytocin augmentation (2% v 13%, p less than 0.001), and fewer infants admitted to neonatal intensive care (p less than 0.10). Of the women who had an uncomplicated labour and delivery requiring no interventions, those with a companion had a significantly shorter duration of labour (7.7 hours v 15.5 hours, p less than 0.001). This study suggests that constant human support may be of great benefit to women during labour.