As a clinical tool to evaluate autonomic dysfunction, "Valsalva ratio" was measured in 36 Parkinson's disease patients (15 men, 21 women) and 10 control subjects (4 men, 6 women). In this study, the Valsalva ratio was defined as the ratio of peak to nadir heart rate during Valsalva maneuver, namely voluntary and transient breathholding in maximal inspiration state with subsequent release by the subject. EKG was monitored throughout the whole process to observe the moment to moment change of heart rate. The subject group with Parkinson's disease was subdivided by clinical variables including sex, are, Hoehn and Yahr clinical stage, duration of symptoms, and duration of therapy with L-dopa containing drugs. The Valsalva ratio of the subject group as a whole was less than that of the control group (P<0.05). But the differences of Valsalva ratio between the subgroups graded by above clinical variables of Parkinson's disease were not statistically significant. The clinical applicability of "Valsalva ratio" measurement described in this study was discussed.