The prefrontal cortex, caudate nucleus, and their dopaminergic innervations have been implicated in complex information processing. The present study utilized the in vivo microdialysis technique to characterize the extracellular dopamine levels in the prefrontal cortex and the caudate nucleus in the rhesus monkey. Basal levels of dopamine were consistently found in the caudate nucleus, while levels in the prefrontal cortex were less reliably measured. Manipulation of dopamine levels using tetrodotoxin and high potassium demonstrated that dopamine measured was dependent on neuronal firing. Administration of indirect dopamine agonists d-amphetamine and cocaine into the prefrontal cortex and the caudate nucleus increased extracellular dopamine levels 250% and 5000%, respectively. Amphetamine and cocaine had greater effects on dopamine levels in the caudate than in the prefrontal cortex. Cocaine induced increases appeared to be less than that of amphetamine and the actions of cocaine lasted longer than amphetamine. This study demonstrates the feasibility of using in vivo microdialysis in monitoring neurochemicals in different regions of the rhesus monkey brain.