Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide. A growing body of evidence suggests that mitochondrial dysfunction and inflammation plays a crucial role as a pathogenetic mechanism in PD. The aim of the present study was to investigate the metabolic profile of PBMCs from PD patients and to search for a possible relationship be-tween cellular bioenergetics and YKL-40. Materials and methods: The study included 18 naïve PD and an age-matched control group (HC, n=7). Patients were diagnosed according to the MDS-PD, the UPDRS and the Hoen–Yahr scales. Mitochondrial activity was measured by a metabolic analyzer on isolated PBMCs from PD’s patients. Gene (qPCR) and protein (ELISA) expression levels of YKL40 were investigated. Results: New data are reported revealing changes in mito-chondrial activity and YKL-40 levels in PD patients. Bioenergetic parameters showed increased respiratory reserve capacity in the PD compared to HC. The protein levels of YKL-40 were three-fold higher in PD. We found a correlation between YKL-40 protein levels and basal respiration and between YKL-40 and ATP production. Conclusion: These observations suggest an interplay between YKL-40 and mitochondrial function in PD. We assume that YKL-40 gene and protein levels in combination with changes in mitochondrial function might serve as an additional tool to monitor the clinical course of PD.