When the sensory block level (SBL) is >= T5 or T4, a high incidence of hypotension occurs in parturients after spinal anesthesia. A rapidly ascending SBL is another risk factor for spinal anesthesia-induced hypotension. However, the relationship between the ascension rate of the SBL and spinal anesthesia-induced hypotension remains unclear. After placement in the left lateral position, combined epidural-spinal anesthesia was performed on 140 parturients undergoing caesarean section using the following procedure: no volume preloading, injection site of L3-4 or L4-5, injection rate of 0.1 mL/sec, and administration of 10mg of 0.5% hyperbaric bupivacaine. A receiver-operating characteristic curve was built to estimate the accuracy of the SBL ascension rate in detecting spinal anesthesia-induced hypotension. The mean time interval from spinal injection to placement in the supine position was 136 +/- 10seconds in all anesthesia procedures. The earliest and most complete records of the SBL started from the 3rd minute after spinal injection. The threshold spread rate corresponding to the highest accuracy for occurrence of hypotension was an SBL of >= T8 at the 3rd minute after spinal injection, with 82% and 88% sensitivity and specificity, respectively. The ascension rate of an SBL of >= T8 at the 3rd minute after spinal injection is as a predictor of hypotension in parturients.