Loss of striatal dopamine (DA) transporters in Parkinson's disease (PD) has been accurately assessed in vivo by single-photon emission tomography (SPET) studies using [123I]beta-CIT. However, these studies have also shown that adequate imaging of the striatal DA transporter content can be performed only 20-30 h following the injection of [123I]beta-CIT, which is not convenient for routine out-patient evaluations. Recently, a new ligand, N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl) tropane (FP-CIT), became available for in vivo imaging of the DA transporter. The faster kinetics of [123I]FP-CIT have been shown to allow adequate acquisition as early as 3 h following injection. In the present study, loss of striatal DA transporters in five non-medicated PD patients was assessed on two consecutive SPET scans, one with [123I]beta-CIT (24 h following injection) and one with [123I]FP-CIT (3 h following injection). The ratios of specific to non-specific [123I]FP-CIT uptake in the caudate nucleus and putamen were consistently 2.5-fold lower than those of [123I]beta-CIT. However, when the uptake ratio of both ligands in these brain regions of patients was expressed as a percentage of the uptake ratio found in healthy controls, both the decrease and the variation of the data were similar. It is concluded on the basis of these findings that [123I]FP-CIT seems as good as [123I]beta-CIT for the assessment of the dopaminergic deficit in PD. The faster kinetics of [123I]FP-CIT are a clear advantage.