BACKGROUND: Parkinson’s disease (PD) is a multisystem-progressive neurodegenerative disease characterized by dopaminergic neurons, however, the role of the non-dopaminergic system (such as melatonin hormone) in the pathogenesis of PD is now emerging.

OBJECTIVE: To identify any potential correlation between the dopamine and melatonin serum levels, and motor, cognitive, and sleep dysfunctions in patients with PD.

METHOD: Cross-sectional piloting study conducted with a sample of 34 patients with PD (aged 50–72 yrs old). Correlation tests performed to identify any potential correlations between the biomarkers’ serum levels and motor, cognitive, and sleep dysfunctional levels in “on-medication” status.

RESULTS: Spearman’s test showed significant correlations between the melatonin serum level and sleep dysfunctions including overall sleep quality (P= 0.010) and subjective sleep quality sub-score (P= 0.001). On the other hand, spearman’s test showed significant correlations between the dopamine serum level and motor dysfunctions including Berg Balance Scale (P= 0.026), 10-Meter Walk Test (P= 0.016), and Fear of Falling Index (P= 0.007), as well as comparisons between the dopamine serum level and cognitive dysfunction (P= 0.048). CONCLUSIONS: Melatonin serum level would serve as a potential biomarker in understanding the PD pathogenesis, and the melatonin serum level should be considered in future studies related to PD besides the dopamine serum level.