The work provides an overview of the current state of research in the entire field of psychoneuroimmunology, with a particular focus on immunological mechanisms in endogenous psychoses. Special attention is given to the cellular immune system and the HLA system. The studies show that signs of immune activation can be found in individuals with schizophrenia and affective psychoses. Diagnostic specificity, the autoimmune hypothesis, and the virus hypothesis are central to the discussion.