A deficiency of dopamine in the striatum may contribute to the decline in motor function associated with aging. We examined the effect of aging on the densities of the D1 and D2 dopamine receptors, their high-agonist affinity sites, and the dopamine uptake sites in postmortem human putamen (n = 32; age range, 19-88 years). With aging a steady decrease was seen in dopamine uptake sites (p less than 0.001), confirming previous morphometric and biochemical data of an age-related loss of nigrostriatal axons. In contrast, the concentrations of the D1 and D2 dopamine receptors and their high-agonist affinity sites, which are believed to represent the functionally active receptors, were not affected by the aging process. These results may have implications for the pharmacological treatment of the age-related decline in motor function.