Objective: The two neurodegenerative disorders namely Parkinson’s disease (PD) and Multiple System Atrophy of the Parkinsonian type (MSA-P) tend to show similar clinical features of Parkinsonism. These disorders also present with autonomic dysfunctions, frequently manifesting as orthostatic hypotension (OH), (42-58% in PD [1] and 80% in MSA-P show OH [2]). The mechanism of OH in PD is proposed to be due to baroreflex failure (central or peripheral lesions) while in MSA-P it is only due to central lesions [3]. We hypothesized that the baroreflex independent vascular reactivity may also be different in them. To evaluate this we assessed sympathetic vascular reactivity to standard cold pressor test in these patients. Methods: The diagnosis of PD was done according to the UK Parkinson’s disease Society Brain Bank Clinical Diagnostic Criteria and MSA-P was based on the Second Consensus Statement for diagnosis of MSA-P. Data was recorded in 8 patients of PD and 9 patients of MSA-P, both with documented OH. ECG and PPG (photoplethysmography) signals were continuously acquired during a baseline period (1 min) and during 10 degree C cold exposure (1 min) of the contralateral hand. The vascular response was evaluated by measuring the pulse transit time and amplitude of the finger-photoplethysmography (PPG) waveform [4]. Analysis was done by an unpaired t test. Results: The Pulse Transit Time (PTT) decreased in patients of both PD (192.7±3.225 ms vs 199.4±1.639 ms, p = 0.09) and MSA-P (195.23±6.4ms vs. 198.00±6.08 ms, p = 0.7). The patients of PD showed significantly larger decrease in PTT as compared to MSA-P (-7.78±2.06 ms vs -2.81±0.98, p=0.03). During the cold pressor test the amplitude of PPG decreased in both patient groups but the percentage decrease was greater in patients of PD than in MSA-P (51% vs. 46% respectively). Conclusion: The vascular reactivity to cold pressor test in patients of MSA-P is lesser than that of PD. The increase in vascular tone (decrease in PTT) during CPT is preserved in PD but significantly lost in MSA-P. Thus the preliminary study shows that baroreflex independent vascular reactivity is significantly different in the patients of PD and MSA-P with documented OH.