The density and distribution of sulfide-silver staining in the neostriatum of 3-, 12-, and 24-month-old male Sprague-Dawley rats were analyzed using the neo-Timm sulfide-silver histochemical technique associated with microdensitometry. This technique stains zinc-containing terminals in the striatum and the density of neo-Timm staining is considered to be parallel to the density of synaptic boutons containing zinc. In the neostriatum sulfide-silver, staining was intense in the matrix, although the striosomes did not show appreciable reactivity. The density of sulfide-silver staining was significantly reduced (p less than 0.001) in the matrix of 12-month-old in comparison to 3-month-old rats. No further changes were noticeable between 24- and 12-month-old rats. In contrast, the area and the perimeter of neostriatum that were assessed by quantitative image analysis did not show age-related changes. The present results indicated that similar to the observations for a variety of neurochemical parameters of rat neostriatum such as local cerebral glucose utilization, cholinergic muscarinic receptors, and dopamine D-1 receptors, zinc-containing striatal terminal were primarily decreased between young and adult subjects but not between adult and aged animals.