The analgesic and respiratory effects of epidural 0.5% bupivacaine were studied in four groups of patients (n = 170) undergoing percutaneous nephrolithotripsy (PNL). Group 1 patients (n = 42) received 0.5% bupivacaine. Group 2 patients (n = 42) received 0.5% bupivacaine with 1:200,000 epinephrine. Group 3 patients (n = 42) received 0.5% bupivacaine plus 100 micrograms epidural fentanyl, and Group 4 patients (n = 44) received 0.5% bupivacaine plus fentanyl plus epinephrine. Intraoperative pain occurred in anatomically adequate segmental blockade in 15 patients from Groups 1 and 2, but in none from Groups 3 and 4. Analgesia was restored by 100 micrograms epidural fentanyl, and motor block appeared to be enhanced. The addition of epinephrine increased the intensity of motor block but not analgesia. Respiratory frequency was slower and respiratory rhythm more irregular in Group 3 than within the other groups. SaO2 decreased to 89% or lower in eight cases, and oxygen supplementation was required. It is concluded that PNL may be safely conducted under epidural analgesia when reinforced by epidural fentanyl while breathing air, provided SaO2 is monitored continuously; otherwise, oxygen supplementation should be provided.