BACKGROUND: Combined spinal-epidural anesthesia has been used to reduce the side effect of spinal or epidural anesthesia. The epinephrine test dose to prevent intravascular injection of local anesthetics after subarachnoid block has not been clearly understood. The purpose of present study is to see the efficacy of simulated intravenous test dose during subarachnoid block. METHODS: 20 ASA physical status 1 and 2 patients underwent subarachnoid block with tetracaine 10 mg in hyperbaric solution at the L3-4 interspace and were divided into two groups, Group 1 (n=10) and Group 2 (n=10). 3 ml of Normal saline was injected intravenously to group 1, while 1:200,000 epinephrine 3 ml (15 microgram) was injected intravenously to group 2 at regression of sensory block to T8-10. 1:200,000 epinephrine 3 ml (15 microgram) was given to each volunteer (Group 3, n=10). Heart rate (HR) was measured at 15 seconds intervals for 3 minutes and systolic blood pressure (SBP) was measured at 1 minute intervals for 5 minutes. RESULTS: SBP increased significantly in group 2 and group 3 at 1 minute after epinephrine test dose injection. Maximal HR changes was 39.7 3.7 beat per minute in group 2 and 25.8 5.2 beat per minute in group 3. There was 100% incidence of detection of intravascular injection of 15 microgram epinephrine in both group when HR increase > or = 20 beats per minute is regarded as positive response. CONCLUSIONS: This study demonstrates that the epinephrine test dose is useful method to detect intravascular injection of local anesthetics either in the combined spinal-epidural anesthesia or epidural anesthesia. The heart rate response after injection of epinephrine was greater than the blood pressure response.