Fifty asthmatic patients and 20 healthy control subjects, carefully age- and sex-matched, were subjected to seven standardized tests to evaluate their autonomic status. Due care was taken to remove factors which could interfere with results. Of the tests concerned with the parasympathetic system, the intravenous atropine test (p greater than 0.10) and heart rate response to standing (p greater than 0.01) which measured the basal parasympathetic tone, did not show a significant difference. Tests requiring stimulation of the parasympathetic system, ie, deep breathing test (p less than 0.001), Valsalva maneuver (p less than 0.001), and carotid sinus massage (p less than 0.001) showed significantly heightened response. Postural fall of blood pressure (p greater than 0.10) and sustained hand grip test (p greater than 0.10), chiefly concerned with the sympathetic system, did not show a significant difference. Of the 50 asthmatic patients, nine were atopic and 41 nonatopic. When the results were compared in the two groups separately, we found that there was no alteration in the measurements except the intravenous atropine test which showed heightened response with atopic subjects (p less than 0.05). These results suggest that hyperresponsiveness of the parasympathetic system is an important factor in producing bronchial spasm in asthmatic patients, and atopic and nonatopic subjects do not differ much in their autonomic status.