Dopaminergic synaptic function may be assessed either at the presynaptic terminal or at the postsynaptic binding sites using molecular in vivo imaging methods. Apart from the density of binding sites, parameters such as alterations in dopamine synthesis, dopamine storage or dopamine release can be quantified either by application of specific radiotracers or by assessing the competition between the exogenous radioligand and endogenous dopamine. Investigations of humans in both clinical and experimental settings have yielded evidence that disturbances of dopaminergic function may be associated with numerous neurological and psychiatric conditions, among which are movement disorders, schizophrenia, attention-deficit hyperactivity disorder, depression and drug abuse. This article gives an overview of those studies, which so far have been performed on dopaminergic neurotransmission in humans using in vivo imaging methods. We focus on disease-related deficiencies within the functional entity of the dopaminergic synapse. Taken together, in vivo findings yield evidence of presynaptic dysfunctions in Parkinson's disease with decreases in striatal dopamine synthesis, dopamine storage, dopamine release and dopamine transporter binding. In contrast,'Parkinson plus' syndromes (multiple system