To develop a regimen that would provide good analgesia after cesarean section with minimal side effects in the setting of prolonged (> 24 h) epidural infusion, buprenorphine or fentanyl was combined with 0.03% bupivacaine in a double-blind study of 23 parturients. Patients were randomly assigned to two groups: group I (n = 12), patient-controlled analgesia by epidural infusion of buprenorphine (3 micrograms/mL) with 0.03% bupivacaine; group II (n = 11), patient-controlled analgesia by epidural infusion of fentanyl (2 micrograms/mL) with 0.03% bupivacaine. Plasma for determination of opioid concentrations was obtained at intermittent intervals. Pain relief was similar and satisfactory in both groups. The median overall satisfaction score was higher (10.0 vs 7.5; P < 0.03) for group II. Pruritus was mild in most patients. Nausea and vomiting, which were most disturbing to the patients, were seen only with buprenorphine. No patient had a respiratory rate of < 12 breaths/min. Mean plasma opioid concentrations did not exceed 1 ng/mL during the study. However, four patients (33%) in group I and six patients (55%) in group II experienced sensory loss in the lower extremities, which made ambulation difficult. One patient in each group developed extensive pressure blisters on both heels. These complications led us to terminate the study. We conclude that 0.03% bupivacaine used in combination with an opioid in prolonged epidural infusions produces a high incidence of sensory loss in the lower extremities and is unsuitable for situations in which early ambulation is desired.