Continuous epidural infusion of bupivacaine with the opioid fentanyl represents an effective analgesic method in the therapy of strong postoperative pain after major surgery. Preparation of the required infusion solution in syringes with a volume of 50 ml immediately prior to administration is routinely performed by nursing staff in Germany. The effort required for the preparation is associated with logistical and pharmaceutical difficulties. The preparation of a mixture of bupivacaine hydrochloride 0.06% and fentanyl 0.0002% in 250 ml infusion bags at the pharmacy of the University Hospital Mainz is described. To determine the physicochemical stability, the concentration of bupivacaine-HCl and fentanyl was assessed using HPLC over a period of 32 days; in addition the pH values were determined. After 32 days 95% of the bupivacaine hydrochloride and fentanyl baseline values were recorded. The pH baseline value had decreased from 5.48-5.52 to 0.5-0.7 units. The measured values confirm the physicochemical stability of the mixture of bupivacaine hydrochloride 0.06% and fentanyl 0.0002% over a period of 32 days. The infusion bag can be stored for 4 weeks at room temperature.