OBJECTIVES: Abnormalities in neurotrophic factors that regulate neuronal development and synaptic plasticity are often implicated as some causes of schizophrenia. In previous studies, researchers reported that brain and serum BDNF levels underwent similar changes during maturation and aging processes in rats. They also found a positive correlation between serum and cortical BDNF levels. In this study, we investigated whether the serum levels of BDNF in Korean schizophrenic patients would be different from those of healthy controls. METHODS: Using an ELISA kit, serum BDNF levels were assessed in schizophrenic group(N=49) and control group(N=50). RESULTS: Serum BDNF levels in the schizophrenic group(36.29+/-19.78ng/ml) were significantly higher than those in control group(22.4+/-14.4ng/ml). The BDNF levels did not correlate with duration of treatment, age or daily dose of antipsychotics in patients with schizophrenia. CONCLUSIONS: This result suggests that schizophrenia is characterized by high serum BDNF levels and supports the hypothesis of neurotrophic factor involvement in psychotic disorder. Serum BDNF level is likely to be one of the possible biological markers for schizophrenia.