Objectives: To compare the clinical efficacy of hyperbaric 0.5% ropivacaine and 0.5% bupivacaine in subarachnoid blockade for ambulatory surgery., Material and Method: Randomized double-blind study of 90 patients undergoing lower abdominal surgery. Subarachnoid blockade was achieved with 0.5% ropivacaine (12.5 mg) or 0.5% bupivacaine (12.5 mg) in 10% glucose. We recorded age, sex, weight, latency, extension of motor and sensory blocks, duration of surgery, side effects and quality as perceived by the surgeon and the patient., Results: The two groups were similar with respect to latency time and extension of sensory block. Durations of motor (68.9 +/- 22.9 min) and sensory (127.0 +/- 24.3 min) blocks were significantly shorter with ropivacaine than with bupivacaine (133.3 +/- 29.4 and 174.9 +/- 25.5 min, respectively). Patients in the ropivacaine group also experienced a less intense motor block (Bromage 1, 11.1% vs. 93.3%) and fewer episodes of hypotension 0% vs. 17.7%) or bradycardia (4.4% vs. 8.8%) than those in the bupivacaine group. No neurotoxic effects or instances of postdural puncture headache were recorded., Conclusions: Hyperbaric 0.5% ropivacaine offers certain advantages over hyperbaric 0.5% bupivacaine for subarachnoid block in outpatient surgery. Duration and intensity of the sensory-motor blockade is less with ropivacaine and fewer cardiovascular side effects develop.