Findings from preclinical studies suggest that treatment with probiotics increased glucose metabolism (increased secretion of glucagon-like peptide-1), reduced peripheral and central inflammation (reduced interleukin-6 and tumor necrosis factor-α (TNF-α)), reduced peripheral and central oxidative stress (reduced peripheral superoxide anion levels and increased central antioxidant glutathione levels), decreased neurodegeneration (increased numbers of tyrosine hydroxylase dopaminergic neurons and levels of brain-derived neurotrophic factor), increased motor function (increased motor agility) and non-motor function (decreased memory deficits). Similarly, findings from clinical studies suggest that probiotics increased glucose metabolism (reduced insulin resistance), reduced peripheral inflammation (reduced peripheral TNF-α expression and C-reactive protein levels), and increased motor and non-motor function (decreased overall PD symptomatology and constipation); however, findings on oxidative stress were inconclusive across studies. Overall, this review is the first one to systematically report evidence for the putative beneficial effects of probiotics on molecular and cellular mechanisms, as well as behavioural phenotypes, in either preclinical or clinical studies in PD. However, additional and more robust studies are still needed to confirm these outcomes, and should aim to focus more on bench-to-bedside investigations, in order to address the existing gaps between preclinical and clinical findings in this field. CLICK TO REVIEW