Abstract: Monoamine transporters are proteins mainly located on nerve terminals of dopaminergic, noradrenergic and serotonergic neurons. They are members of a larger sodium dependent transporter family and represent a major mechanism terminating the action of released neurotransmitter in the synaptic cleft. In addition to being important target molecules for many antidepressive drugs and substances of abuse, transporter proteins are good markers for the integrity of monoaminergic innervation. Therefore, there is a growing interest for in vivo imaging studies using positron emission tomography (PET) or single photon emission computed tomography (SPECT) and ligands selective for monoamine transporters. In this review, the use of monoamine transporter ligands (or tracers) for imaging studies of cocaine dependence, neurodegenerative diseases and mechanism of antidepressant drug action is discussed, with special focus on the use of PET for evaluating possible new pharmacological innovations.