A case of acute lithium intoxication is presented in which plasma levels of 3-methyoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA) were longitudinally measured during the intoxication period. Plasma levels of MHPH and 5-HIAA, but not HVA were increased during the intoxication period. These results suggest that toxic levels of lithium concentration occurred due to transient enhancement of serotonin and noradrenaline function. Dopamine function was not affected. Copyright 2000 John Wiley & Sons, Ltd.