This study was designed to investigate under controlled conditions sensory and motor blockade provided by epidural anaesthesia following two concentrations of bupivacaine without adrenaline. Twenty four patients received for extracorporeal shock wave lithotripsy a lumbar continuous epidural anaesthesia randomized with bupivacaine 0.75% (n = 12) or 0.5% (n = 12). During development and regression, sensory blockade was determined by the pinprick method, motor blockade by the Bromage score. All differences between the two concentrations--even though not all statistically significant--spoke in favour of bupivacaine 0.75%: shorter time of onset, more cephalad spread, higher intensity and longer duration of sensory and motor blockade. The higher concentration should be injected more slowly due to the increased risk if intravascular injection should occur; it should not be used for cesarean section.