The painful stimuli produced by a new generation of electrohydraulic/electromagnetic lithotripters are such that continuous infusion analgesia rather than general or regional anesthesia is appropriate. We describe our experience with continuous alfentanil infusion supplemented with intravenous bolus midazolam in caring for patients treated with an unmodified Medstone STS 1050 lithotripter. Ninety consecutive treatments using this technique averaged 63 minutes, compared with 69 minutes for 14 treatments done with general anesthesia and 88 minutes for 58 treatments done with epidural anesthesia. The stone burden, kilovoltage, and number of shocks were similar for the three groups, as was the immediate stone fragmentation rate. Only 2 of 90 patients received inadequate analgesia with the intravenous technique and required the induction of general anesthesia. Continuous-infusion analgesia appears sufficient to blunt the stimulus provided by the unmodified spark-gap lithotripters still in common use.