BACKGROUND: The purpose of this study was to compare the onset time, degree and duration of motor block, and the satisfaction of surgeons of given single epidural injections of 1.0% ropivacaine and 0.5% bupivacaine in patients undergoing hip arthroplasty surgery. METHODS: In a double-blind randomized study involving 20 patients, patients randomly received 12 ml of 1.0% ropivacaine or 0.5% bupivacaine at the L2 - 3 or L3 - 4 interspace. Parameters measured were the onset time, duration and degree of motor block, and the satisfaction of the surgeons. RESULTS: Mean onset time of Bromage scale 2 was significantly slower with 1% ropivacaine (14.6 +/- 1.3 min) than with 0.5% bupivacaine (15.7 +/- 2.0 min). However, each frequency of motor blockade (Bromage scale 1, 2 and 3) with 1.0% ropivacaine (10, 8 and 7) was greater than that seen with 0.5% bupivacaine (7, 6 and 1). For scales 1 and 2, 1.0% ropivacaine had a significantly longer duration than 0.5% bupivacaine and the overall duration of motor blockade with 1.0% ropivacaine was longer than 0.5% bupivacaine. Motor block was in 80% achieved satisfactorily of the ropivacaine group and 60% of the bupivacaine group by the surgeons. CONCLUSIONS: In conclusion this study demonstrated that 1.0% ropivacaine provides a more rapid onset time, greater degree and longer duration of motor block without unacceptable side effects than 0.5% bupivacaine for hip arthroplasty surgery. From these results, it may suggest that 1.0% ropivacaine may be useful for lower extremity orthopedic surgery requiring good muscle relaxation.