Pramipexole has been shown to possess neuroprotective properties in vitro that are partly independent of its dopaminergic agonism. The site of neuroprotective action is still unknown. Using [3 H]pramipexole, we show that the drug enters and accumulates in cells and mitochondria. Detoxification of reactive oxygen species (ROS) by pramipexole is shown in vitro and in vivo by evaluating mitochondrial ROS release and aconitase-2 activity, respectively. Pramipexole and its (ϩ)-enantiomer