Acute emotional arousal, regardless of the emotional state, increases sympathetic activity. The sympathetic response, however, does not lead to a uniform change in all sympathetically innervated systems. The response magnitude of specific systems, such as the cardiovascular system, depends to a large extent on constitutional and hereditary factors. The subjective awareness of bodily changes accompanying heightened sympathetic activity is inaccurate; people often recognize the direction but not the degree of change. The level of body awareness depends on various psychologic factors, of which anxiety plays an important role. Acute stress produces sympathetic activation in nonanxious as well as anxious persons. Nonanxious persons tend to have more flexible autonomic responses. They show stronger responses to novel situations but return to lower autonomic levels earlier and habituate faster than do anxious persons. That is, nonanxious persons possess a greater autonomic flexibility than anxious persons. It is important to know the physiologic state of anxiety disorder patients during periods when they do not feel anxious, during times of heightened tension, during the performance of standardized stress tasks, during exposure to psychopathology-specific stressors, and during "spontaneously" occurring surges of anxiety, such as panic attacks. At present only limited information concerning these conditions is available. There is little evidence that anxiety disorder patients, perhaps with the exception of very severe cases, have an increased sympathetic tone when they do not feel anxious. However, all anxiety disorders, with the exception of simple phobia, show some sort of physiologic activation in threatening situations, including the recording of physiologic baseline values in laboratories. The type of activation differs among anxiety disorders. During periods of rest, social phobics and panic disorder patients tend to show sympathetic activation, generalized anxiety disorder patients show increased muscular tension without sympathetic activation, and obsessive-compulsive patients show increased muscular tension along with sympathetic inhibition. Under laboratory stress, both normals and anxiety disorder patients react with sympathetic arousal. However, in generalized anxiety and obsessive-compulsive patients the response is weaker than in normals, suggesting the presence of an inhibitory process. Thus, the autonomic flexibility of anxiety disorder patients is reduced.(ABSTRACT TRUNCATED AT 400 WORDS)