BACKGROUND: The stellate ganglion block controls the pain and the vascular insufficiency in the innervating regions. Recently, the therapeutic indications of the stellate ganglion block are widely extended to the psychosomatic disorder. Therefore, this study was designed to observe the effect of the stellate ganglion block on stress using the Porsolt's behavioral despair model of rats. METHODS: Fifty-five male Sprague-Dawley rats were given five forced-swimming tests at 24-hour intervals. The first test through which rats learn helplessness lasted 15 minutes and following four tests given 30 minutes after every superior cervical ganglion block lasted 5 minutes respectively. The superior cervical ganglion block was achieved by using 0.2 ml of 1% lidocaine in the experimental group(n=30), and 0.2 ml of normal saline instead of lidocaine in the control group(n=25). The duration of mobility was measured during the first 5 minutes in all tests. RESULTS: A difference was found between the control and the experimental group in the performance ratios after the superior cervical ganglion block(P<0.01), but the number of trials of the superior cervical ganglion block did not effect the duration of mobility. CONCLUSIONS: These results suggest that the superior cervical ganglion block reduces the duration of immobility independently of the number of trials of the superior cervical ganglion block.