New patient-controlled analgesia devices can deliver an analgesic by continuous infusion along with demand dosing. This prospective investigation involving postcesarean-section patients was undertaken to determine whether a combination of continuous infusion and demand dosing of meperidine would provide more effective analgesia than would demand dosing alone during the first 24 hours. During a 12-month period, 171 patients were prescribed meperidine postoperatively, using a 5- to 10-mg demand dose no more frequently than every 10 minutes. Patients were assigned to groups receiving no continuous infusion or infusion at rates of 10, 20, or 30 mg/h. The groups receiving continuous infusion showed more immediate and sustained pain relief, with no serious complications. All patients were able to understand the nurse, became ambulatory, and tolerated liquids on the first postoperative day. The infusion rate of 20 mg/h was most acceptable in requiring fewer demand doses while providing satisfactory pain relief without undesired sedation. In conclusion, a system combining continuous infusion and demand dosing was preferable to demand dosing alone, and added no apparent hazards.