The antipsychotic drug quetiapine increases the firing rate of dopamine neurons in the substantia nigra and the ventral tegmental area of the rat. In the present study we used an in vitro midbrain slice preparation and found that 3 μM quetiapine increases the firing rate of dopamine neuron in both structures by ∼30%. The magnitude of the increase was not correlated with the basal firing rate of the dopamine neurons. In addition, quetiapine was not able to antagonize the inhibition of the firing evoked by the dopamine D2 receptor agonist quinpirole. Only with a very high concentration (30 μM), quetiapine was able to counteract the amphetamine-induced inhibition of the firing of the ventral tegmental area neurons; this effect was less pronounced in substantia nigra neurons. These findings indicate that the increase in firing rate induced by quetiapine cannot solely be mediated through an interaction with the dopamine D2-like autoreceptor present on the dopamine neurons.