[3H]GBR 12935 bound with high affinity to dopamine uptake sites in rat striatum where a close parallelism was observed between the subcellular localization profiles for [3H]dopamine uptake and [3H]GBR 12935 specific binding. Using the same ligand, we characterized the dopamine uptake sites in human striatum: the mean KD value was 3.2 nM and the specific binding was inhibited by several dopamine uptake blockers but with slightly lower affinities than those observed in the rat. The subcellular localization profile revealed a synaptosomal enrichment of the specific binding in human striatum. [3H]GBR 12935 binding was decreased in the putamen and caudate nucleus of subjects with Parkinson's disease (33 and 46% of control values, respectively) and progressive supranuclear palsy (38 and 57% of control values, respectively). It is very unlikely that the remaining binding sites in both diseases correspond to piperazine acceptor sites that are not involved in dopamine uptake. However, we cannot exclude the possibility that some of these remaining dopamine transporter sites are not functional, since the reduction in [3H]GBR 12935 specific binding was less marked than the decrease in the dopamine content of the same areas.