Purinergic system plays a role in the regulation of many psychological processes, including mood and activity. It consists of P1 receptors, with adenosine as the agonist, and P2 receptors, activated by nucleotides (e.g., adenosine 5’-triphosphate – ATP). Propounded disturbances of uric acid in affective disorders were related to the introduction of lithium for the treatment of these disorders in the 19th and 20th century. At the beginning of the 21st century, new evidence was accumulated concerning a role of uric acid in the pathogenesis and treatment of bipolar disorder (BD). In patients with BD, higher prevalence of gout and increased concentration of uric acid have been found as well as the therapeutic activity of allopurinol, used as an adjunct to mood stabilizers, has been demonstrated in mania. In recent years, the research on the role of the purinergic system in the pathogenesis and treatment of affective disorders and schizophrenia focuses on the role of adenosine (P1) receptors and nucleotide (P2) receptors. Activation of adenosine receptors is related to an antidepressant activity. Alterations of P2 receptors are also significant for the pathogenesis of affective disorders. The role of purinergic system in schizophrenia is related to the effect of adenosine and nucleotide receptors on dopaminergic and glutamatergic neurotransmission. A lot of data indicate that schizophrenia is related to a deficit of adenosine system. Changes in the purinergic system are also significant for psychopathological symptoms of schizophrenia and for the action of antipsychotic drugs.