The effect of thallium acetate administration on monoaminergic pathways was studied in male Wistar rats using 30 mg/kg and 50 mg/kg acute IP doses. We found that thallium activated both monoamine oxidase (MAO) activity and serotonin turnover rate in rat brain regions, that may contribute to the neuronal damage mechanism of the agent. MAO activity in midbrain and pons was increased at both doses (at 30 mg/kg dose by 27.7% and 37%; at 50 mg/kg dose by 48% and 47%, respectively vs. control group). Serotonin turnover rate in pons was also increased at the 30 mg/kg dose (172%) while midbrain and pons serotonin turnover was increased only at the 50 mg/kg dose (56% and 166%, respectively vs. control group). Dopamine turnover rate was not significantly changed. The results indicate that thallium induced a significant increase in pons and midbrain MAO activity and also in serotonin turnover rate as compared with control animals, and this could led to behavioral and toxic alterations in the rats intoxicated with thallium.