The binding of [3H]GBR-12935 to dopamine (DA) uptake sites was studied in post-mortem putamen from a control group and from patients with Parkinson's disease (PD) or dementia of the Alzheimer type (DAT). The specific binding (Bmax) was almost completely abolished in the PD group and reduced by 65% in the DAT group. There were no significant differences in apparent binding affinity (Kd) between the DAT group and controls. The decreases in [3H]GBR-12935 binding to DA uptake sites in this study indicate a marked degeneration of DA neurites in the putamen in PD and also in DAT.