Sudomotor function tests provide information on the activation of the sympathetic efferent fibers. We have studied the efficacy of stellate ganglion block (SGB) by assessment of changes in perspiration of the thumb in 10 patients. SGB was performed at C7 with 6 ml of 1% mepivacaine, and perspiration was induced by mentally stressful conversation and having patients draw up their knees for physical stress. Suzuken Kenz Perspiro OSS-100 was used for quantitative detection of perspiration. The value before SGB was 1.49 +/- 0.46 mg.3 min-1, and it showed a statistically significant decrease to 0.73 +/- 0.33 mg.3 min-1 10 min after SBG (P < 0.01). The present study suggests that quantitative measurement of perspiration is useful to judge the effects of SGB on arm.