The caudate putamen is a neurochemically and functionally heterogeneous nucleus. Understanding the correlation between these regional variations in neurochemistry and function could greatly aid in the treatment of neurological disorders associated with this area of the brain. Since dopaminergic dysfunction has been implicated in some of these disorders, regional variations in the neurochemistry of this transmitter system are of particular interest. The dopaminergic response to 2.5 mg/Kg D-amphetamine was examined by in vivo voltammetry in 7 dorsal and 7 ventral regions of the caudate-putamen in the urethane anaesthetized rat. Extracellular dopamine concentration increased in all the areas examined. However, the effect was regionally heterogeneous-areas separated by as little as 1 mm showing significantly different responses in terms of both the absolute change and the rate of change in dopamine concentration. A significant general trend was also evident. Amphetamine produced an increasing effect in extracellular dopamine concentrations in the dorsal and lateral areas of the nucleus. It was concluded that the regionally heterogeneous effects of amphetamine on extracellular dopamine could be attributed to regional variations in the density of dopamine transport sites within the caudate-putamen. Since this transport site is the site of entry of a number of neurotoxins this finding may contribute to our understanding of the functional loss associated with disorders such as Parkinson's disease.