Comment: A simple method for assessing acute changes in the activity of the sympathetic nervous system would be useful for monitoring regional anesthesia or evaluating patients with sympathetically maintained pain. Galvanic skin response has been used in the past but has not been found to be completely satisfactory. Thermography is easily performed but designed for large areas of the body. Laser doppler flowmetry used to measure skin perfusion is a promising new technique. Previous studies have shown it can detect changes in skin perfusion in patients with regional anesthesia or autonomic dysfunction. The current study indicates that it can reliably detect changes in skin perfusion caused by known reproducible stimuli that provide a sympathetic response.