BACKGROUND: Subhypnotic doses of propofol have been demonstrated to possess a direct antiemetic property. The present study was designed to assess the antiemetic efficacy of propofol mixed the reservoir bag of an intravenous patient-controlled analgesia (PCA) in patients using an intravenous PCA after a thoracotomy. METHODS: One-hundred seventy five subjects were allocated to two groups. Propofol was added to the PCA regimen to a concentration of 5 mg/ml in group P. The same volume of normal saline were substituted for propofol in group C. The PCA regimen was composed of ketorolac, fentanyl and morphine. The dosages of drugs were adjusted according to the patient's age and sex. The PCA was set at a basal rate of 0.5 ml/hr, bolus dose of 1 ml and a lockout interval of 10 min. The incidence and severity of PONV, sedation, pain and other side effect was assessed at 1, 4, 8, 12, 18, 24, 36, 48, 60 and 72 hr postoperatively. RESULTS: There was no significant difference in the incidence and the severity of postoperative nausea and vomiting (PONV) between the two groups. Overall pain scores were not different between the two groups. The occurrence and the severity of sedation was significantly higher in group P compared to group C (P < 0.05). CONCLUSIONS: Propofol added to a concentration of 5 mg/ml in a PCA regimen, composed of ketorolac, fentanyl and morphine, used for postoperative pain control is not effective in decreasing PONV in patients undergoing a thoracotomy.