Lithium (Li) is a typical mood stabilizer and the first-line treatment of bipolar disorder (BD). Despite the extensive clinical use, suggested mechanisms of Li action remain widely different and debated. Additionally, no reliable markers exist for diagnosis, monitoring, treatment selection and prognosis of BD. In our laboratory, we are testing changes induced by therapeutic Li concentration in different types of biological samples with the main focus on Na+/K+-ATPase as one of the candidate pathways of Li action. To extend the scope of screening of Li-induced alterations of the plasma membrane and its proteins we are also interested in lipid peroxidation products amount and opioid receptor signalling pathways.