We studied the selective block on patients receiving epidural Ropivacain (R) infusion for postoperative analgesia after major abdominal surgery. Twenty patients received R and twenty patients received Bupivacain (B) via peridural catheter during and after surgery. The patients' age ranged between 40 and 80 and they belonged to ASA I, II and III risk group. The epidural catheter was inserted one day before surgery and the proper position was tested by 80 mg Lidocaine. The epidural needle was inserted via T10-L1 interspaces in upper abdominal surgery and through L1-L3 interspaces in lower abdominal surgery. After the operation continuous epidural infusion of 2 mg/ml solution of R or 2.5 mg/ml solution of B was started. The infusion rate was changed according to the grade of sensory and motor block. The following parameters were observed during the postoperative 72 hours: blood pressure, heart rate, arterial blood O2 saturation, modified Bromage (BMG) score, verbal analogue scale (VAS), the spread of sensory block. Satisfactory sensory blockade was achieved with both local anaesthetics. The required daily dose of R and B increased during 72 hours. VAS scores reached their maximum level within 24 hours and were lower in the R group than in the B group but the difference was not significant. We experienced that 0.25% B causes more intense motor block than 0.2% R in equianalgetic dose but the difference did not reach a significant level. The infusion rate was often decreased because of the unwanted motor block caused by 0.25% B leading to insufficient postoperative analgesia. Because of this fact patients receiving B required opioid addition more often. Our conclusion is that R/B relative dose ratio is 1.2 suggesting that these local anaesthetics have different analgesic potency.