Previous neuroimmunological studies focused mostly on depression, regardless of its diagnostic category. In this paper, the studies on the immunological system in patients with bipolar affective illness, including manic episode, have been presented. Research possibilities of neuroimmunology of affective disorders using molecular-genetic methods have also been shown. The studies on the neuroimmunology of depression have always been connected with studies on changes in the immunological system related to stress situations. Disturbances of the immunological system regulation have features of either decrease or pathological increase of the immunological system, with increased activity of pro-inflammatory cytokines (interleukin 1 and 6, interferon). Some pathogenic role for the disturbances of immunological system in depression is also played by viral infections (herpes, Borna viruses). The changes of the immunological system in mania are mostly similar to those observed during depression. An increase of activity of pro-inflammatory cytokines, connected with the lymphocyte Th1 system is especially evident. Like in depression, the role of viral infections has been pointed out (herpes, Borna, parvovirus B19). The oldest mood-stabilizing drug, lithium, has been shown to have strong action against herpes viruses. Molecular-genetic studies point to an association of some genes of the immunological system with both bipolar disorder and schizophrenia. An association of some genes with a predisposition to depression and efficacy of antidepressant drugs has also been shown.