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Background: Epidural meperidine is effective for postoperative analgesia, but the optimum dose has not been evaluated., Methods: Five doses of epidural meperidine (12.5, 25, 50, 75, and 100 mg) given at the first request for analgesia after cesarean section were compared. Visual analog pain scores, duration of analgesia as defined by time to first patient-controlled epidural analgesia demand, plasma concentrations of meperidine, side effects, and subsequent 24-h consumption of meperidine were evaluated., Results: All doses were effective, but patients took longer to become pain-free after 12.5 mg (median 30 min) compared with 25 mg (median 12 min, P = 0.038), and duration of analgesia was shorter after 12.5 mg (median 83 min) compared with 25 mg (median 165 min, P = 0.0005). Increasing dose to more than 25 mg did not improve onset or duration of analgesia. Plasma concentrations of meperidine were less than minimum effective analgesia concentration for all doses except 100 mg. There was more frequent nausea (P = 0.004) and dizziness (P = 0.0002) after 100 mg compared with smaller doses., Conclusions: Epidural meperidine provides effective postoperative analgesia, although of relatively short duration. A single dose of 25 mg is superior to 12.5 mg, but there is no benefit from increasing the dose to 50 mg or greater.