The observation of decline in mitochondrial electron transport chain function, specifically at complex I, in patients with Parkinson's disease (PD) has been reported by several groups. This study investigates whether a defect of mitochondrial function is present in the platelets of PD patients from an Indian population. We found that the NADH dehydrogenase activity in the platelets of PD patients is lower than that in healthy age- and gender-matched controls, while the succinate dehydrogenase activity was similar in both groups. Furthermore, there was no change in either of the activities in patients with Parkinson plus syndrome or atypical parkinsonism. This is the first report indicating a decline in mitochondrial function in the platelets of PD patients from the Indian population, offering further support to the role of a mitochondrial defect in PD.