Epidemiological, clinical and post mortem studies indicate that inflammatory and immune reactions are involved in the pathomechanisms of affective and schizophrenic spectrum disorders. However, in psychiatric patients, only sporadic investigation on immunochemistry has been performed and information about immunofunction derived by investigation of immunocompetent cells in the CSF is not available to date. Here we present an interdisciplinary work of neurologists, psychiatrists and hemato-immunologists focusing on the immunology of psychiatric and neurological disorders. In a first study including 63 patients with therapy resistant affective and schizophrenic spectrum disorders we applied conventional, validated neurological CSF investigation such as analysis of albumin, IgG, IgA, IgM, oligoclonal IgG and specific antibodies, cell count and interpreted the data by Reibergrams. In a second study, we applied the highly sensitive and specific multicolour flowcytometry of paired samples of CSF and peripheral blood cells to characterize the immunostatus of psychiatric and neurological patients. We demonstrate that flowcytometry technology constitutes an appropriate method to investigate subsets of lymphocytes even with low CSF cell numbers, and therefore as a promising diagnostic tool for routine purposes in the differential diagnosis of psychiatric diseases. Furthermore, knowledge of the frequencies of T cell subsets such as the T regulatory cell type might open new avenues to models of psychiatric and neurological diseases as well as diagnostic and monitoring implications.