The aim of this study was to determine the effect on the instrumental delivery rate of two different concentrations of bupivacaine combined with fentanyl in epidural infusions during labour. Only primiparous women in whom a spontaneous vaginal delivery was anticipated, were included in the study. Those women receiving a higher concentration of bupivacaine and therefore a greater amount of local anaesthetic agent during labour were significantly more likely to have an instrumental delivery with Kielland's rotational forceps (p < 0.01). Those women receiving a lower concentration and smaller amount of bupivacaine were significantly more likely to have an instrumental delivery with Neville-Barnes forceps (p < 0.05). This provides evidence to support the theory that epidural analgesia may contribute to inadequate rotation of the presenting fetal part due to weakened pelvic floor muscles and that this is more likely to occur when higher concentrations of bupivacaine are used and a greater degree of motor block occurs.