Schizophrenia is a complex disease with mostly unknown aetiology. Rapid development of molecular profiling technologies in recent years has facilitated identification of physiological processes associated with schizophrenia. In particular, changes have been found in the blood of schizophrenia patients, and this offers an accessible and efficient alternative to brain samples for research purposes. Here, we review the metabolic, immune and hormonal imbalances characterised in subgroups of schizophrenia patients and discuss potential applications in differential diagnosis, prognosis and early intervention. We also describe development of the first validated biological blood test for diagnosis of schizophrenia, and the challenges involved after introduction of this into clinical practice. Moreover, we discuss possibilities for further research on biomarkers for diagnostic applications in schizophrenia. Promising research avenues include extension to functional analysis of blood cells and applications in prediction of drug response and novel drug discovery.