The recent hypothesis about the pathophysiology of schizophrenia has been centered mainly on two theories, i.e. dopamine hypothesis and serotonin hypothesis. We investigate the correlations between plasma monoamine metabolite concentrations and clinical symptoms in schizophrenic patients. The first purpose of our study was to examine whether the plasma levels of HVA(homovanillic acid) and 5-HIAA(hydroxyindoleacetic acid) are significantly different in schizophrenics, compared to normal controls. And, with the intention of clarifying the interaction between dopaminergic system and serotoninergic system, the ratio of HVA/5-HIAA also was measured. The second purpose was whether the basal(pre-treatment) levels of these metabolites show the correlation with clinical symptoms. Finally, third purpose was whether basal HVA and 5-HIAA levels can be held as a predictor of treatment response. We used Scale for the Assessment of Positive Symptoms(SAPS) and Scale for the Assessment of Negative Symptoms(SANS) as the clinical symptom rating scales. Our results were as followed, 1) only the level of basal plasma HVA was significantly differ in schizophrenics. 5-HIAA and HVA/5-HIAA were not. 2) basal HVA showed significant correlation with SAPS score, especially delusion subscale. 3) the higher was the basal HVA level, the more improvement in clinical symptoms was observed. The basal 5-HIAA level and the HVA/5-HIAA ratio did not show any significant findings. These results support the dopamine hypothesis of schizophrenia, but fail to examine on the possible involvement of serotonin in schizophrenia.