The relationships between behavioral responses and levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in brain of mice were investigated after intravenous injection of fumitremorgin A (FTA). The latent periods to the onset of tremor, clonic convulsion, tonic convulsion and death induced by FTA are observed in a dose-dependent fashion. However, the dose-dependency is not observed between levels of 5-HT and 5-HIAA and activities of 5-HT metabolizing enzymes in brain of FTA-treated mice. Insignificant participation of serotonergic mechanism in modulation of those behavioral states elicited by FTA is conclusively suggested.