This article has reviewed the laboratory evaluation of autonomic disorders. Autonomic testing can be divided into the assessment of three functional domains: sudomotor (assessed best by the thermoregulatory sweat test or QSART), cardiovagal (assessed by the Valsalva ratio and heart rate response to deep breathing or standing up), and adrenergic (assessed by the blood pressure response to the Valsalva maneuver or head-upright tilt). Tables 2 and 3 summarize the test findings in a variety of clinical disorders affecting autonomic nervous system function.