BACKGROUND AND OBJECTIVES: Patients undergoing thoracotomy experience severe postoperative pain. This study aimed at evaluating postoperative analgesia with the association of intravenous and epidural morphine as compared to a single route. METHODS: Participated in this study 20 patients of both genders, physical status ASA I, II or III, scheduled for thoracotomy. Patients were premedicated with intravenous midazolam (3 to 3.5 mg) in the OR. Monitoring consisted of continuous ECG, invasive blood pressure, pulse oximetry, capnography, CVP, diuresis and temperature. Continuous epidural anesthesia was induced in T7-T8 with 10 ml of 0.25% bupivacaine followed by fentanyl (5 microg.kg-1), etomidate(0.2 to 0.3 mg.kg-1) and succinylcholine (1 mg.kg-1). Tracheal intubation was performed with a double lumen tube and complemented with pancuronium(0.08 to 0.1 mg.kg-1) and mechanically controlled ventilation. Patients were then randomly distributed in three groups. Group I received 2 mg of 0.1% morphine by epidural catheter at anesthetic induction (M1), 12 h (M2) and 24 h (M3) after surgery. Group II received intravenous morphine by infusion pump (15 microg.kg.h-1) preceded by a 50 microg.kg-1 bolus, for 30 hours. Group III received 0.5 mg epidural morphine in M1, M2 and M3, associated to intravenous morphine by infusion pump (8 microg.kg.h-1), preceded by a 25 microg.kg-1 bolus, for 30 hours. Blood gas analysis, heart and respiratory rate, incidence of pruritus, nausea, vomiting and postoperative analgesia were evaluated at 6-hour intervals for 30 postoperative hours. Analgesia was evaluated by a numeric gradual scale (NGS) from 0 to 10. RESULTS: NGS was lower in Group I in M2, without differences in remaining intervals. Pain decreased in Groups II and III as from 18 hours as compared to baseline and to Group I. Group I needed more additional analgesia as compared to other groups. CONCLUSIONS: There has been a better analgesic effect with intravenous morphine or the association of intravenous and epidural morphine, with lower drug doses. This difference was significant when lower analgesic doses were used in these groups and represented an effective postoperative analgesic method for thoracotomy, with lower respiratory depression and emetic effects.