The effects of epidural anaesthesia with plain 2% lidocaine or mepivacaine were compared in 200 patients undergoing extracorporeal shock wave lithotripsy in a double-blind manner. The onset, spread, duration and quality of analgesia were similar in both groups. The numbers of patients who needed vasoconstrictor or atropine were almost equal in both the lidocaine and the mepivacaine groups. Mild but significant hypotension continued for a longer period in the mepivacaine group than in the lidocaine group. A transient decrease in arterial oxygen saturation was seen in two patients receiving lidocaine and in three patients receiving mepivacaine. Mild systemic toxicity was observed in eight patients in both groups, although serious complications such as convulsions did not occur. It is concluded that both drugs can be used equally safely for epidural anaesthesia, although the maximum recommended doses differ.