OBJECTIVE In the treatment of acute schizophrenia, risperidone and aripiprazole are both placed the first line antipsychotics. These two antipsychotics have different pharmacological effects. We investigated the effects of risperidone on plasma levels of homovanillic acid (HVA) and 3-methoxy-4hydroxyphenylglycol after unsuccessful aripiprazole treatment in acute schizophrenia. METHODS Ten Japanese patients with acute schizophrenia were enrolled to this study. Plasma levels of monoamine metabolites were analyzed with high-performance liquid chromatography with electrochemical detection. RESULTS Risperidone improved the symptoms and 4 of 10 patients were responders. Risperidone showed a tendency to decrease plasma HVA (pHVA) levels in responders (p = 0.068), but not in non-responders (p = 1.0). At baseline, pHVA levels of responders were significantly higher than that of non-responders (p = 0.033). A trend for negative correlation was found between pHVA at baseline and the changes in Positive and Negative Syndrome Scale-Total (p = 0.061, r = -0.61). CONCLUSIONS Our results suggest that high pHVA level before switching may predict good response to the second line antipsychotics after unsuccessful first antipsychotic treatment. If aripiprazole is not effective in acute schizophrenia, switching to risperidone may be effective and reasonable strategy for improving symptoms.