The addition of fentanyl or clonidine to levobupivacaine was evaluated in patients undergoing breast surgery under general anaesthesia with intra- and postoperative paravertebral analgesia. Patients were randomly allocated to four groups: Group L received 19 ml bolus levobupivacaine 0.25% plus 1 ml saline followed by an infusion of levobupivacaine 0.1%; Group LF received 19 ml bolus levobupivacaine 0.25% plus fentanyl 50 microg followed by an infusion of levobupivacaine 0.05% with fentanyl 4 microg x ml(-1); Group LC received 19 ml bolus levobupivacaine 0.25% plus clonidine 150 microg followed by an infusion of levobupivacaine 0.05% with clonidine 3 microg x ml(-1); Group C (control) received general anaesthesia without paravertebral analgesia. All groups received postoperative i.v. morphine patient controlled analgesia (PCA). Although mean (SD) postoperative PCA morphine consumption was decreased in LF [7.9 (4.1) mg] and LC [5.9 (3.5) mg]vs L [27.7 (8.6) mg] or C patients [21.7 (5.5) mg], p < 0.01, paravertebral fentanyl and clonidine were associated with significantly increased vomiting and hypotension, respectively.