The ph-changes of cerebral spinal fluid were measured following subarachnoid injection of bupivacaine 0.5% with and without adrenaline (1:200,000) during the three hours after the start of anaesthesia. At the same time drug precipitation was not detected. The ph-changes however, were pronounced but not enough to cause disturbances of the homoeostatic milieu. Especially no significant differences related to adrenaline were be found. The authors recommend bupivacaine 0.5% with and without adrenaline for spinal anaesthesia.