Biological markers of psychiatric disorders can be employed both for research and clinical purposes, are classified into state, trait, and morbid markers, and are expected to be useful in diagnosis, treatment, and prediction of psychiatric disorders in clinical settings. Near-infrared spectroscopy that can measure reactivity of cerebral cortex function is one of biological markers for clinical purposes, and has revealed characteristic patterns of frontal lobe function in psychiatric disorders. Availability of biological makers for diagnosis of psychiatric disorders was examined by reviewing effect sizes of various biological markers in schizophrenia, showing that more elaborated markers for higher brain functions are promising: cognition (1.0-1.4), neurophysiology (0.8-1.0), functional brain imaging (0.6-0.8), and structural brain imaging (0.5-0.6).