Background. Nicotine is one of the most frequently used drugs of abuse. It has long been speculated that in addition to nicotine , tobacco contains other compounds that reinforce addiction. Two promising candidates are the tobacco smoke constituents, harmane and norharmane. Purpose. Our study evaluated the effects of exposure to harmane and norharmane alone and in combination with nicotine on midbrain neuronal cultures. Experimental design. After 24 h exposure, cytotoxicity, dopamine (DA) levels, pTH, TH, MAO-A, and MAO-B expression levels were investigated. Results. At low-to-moderate doses (1 μM–100 μM), harmane or norharmane exposure caused significant dose-dependent decreases in intracellular DA without causing high rate of cell death, mitochondrial dysfunction or generation of ROS. Har-mane exposure also resulted in subsequent increase in extracellular DA levels. Conclusion. Along with downregulation of protein expression, notably MAO-B, our data indicate the potential of harmane and norhar-mane to act in synergy with nicotine in midbrain neurons.