The primary objective of present study was to evaluate the stability of hydromorphone hydrochloride injection as well as to compare the stability of hydromorphone and morphine under different infusion conditions. Hydromorphone hydrochloride and morphine hydrochloride injections were dissolved in 0.9 % sodium chloride and stored in patient-controlled analgesia pump, glass bottles and ordinary syringes (polyvinyl chloride) at 25 degrees and 37 degrees. The concentrations of 0.05 and 0.025 mg/ml were used, which were clinical conventional intrathecal doses in this hospital. Samples were collected at 0, 1, 2, 3, 5, 7, 9, 11, 13 and 15 days and analyzed using high performance liquid chromatography. At each time point, the appearance and pH values of the solutions were also examined, which indicated that hydromorphone hydrochloride injection and morphine hydrochloride injection stored in the infusion sets made of different materials for 15 d showed no significant changes either at 25 degrees or 37 degrees. The high performance liquid chromatography analysis indicated that the concentrations of both drugs were maintained at greater than 90 % of their initial concentrations on day 0 either at room temperature or body temperature. Hydromorphone hydrochloride injection and morphine hydrochloride injection were stable at least for 15 days when dissolved in normal saline in polyvinyl chloride infusion bag, non-polyvinyl chloride infusion bag and patient-controlled analgesia pump either at room temperature or body temperature.