Several cognitive functions e.g., episodic memory, executive functions, speed of processing deteriorate across the adult life span. A new line of research for understanding these age-related cognitive changes departs from the observation that there are gradual losses in the dopamine (DA) system from early to late adulthood. The importance of DA for higher cognitive functions is well established. In six PET studies, we will investigate pre-and postsynaptic markers of the DA system in the striatum and in extrastriatal regions among young and older adults. In conjunction with the PET assessment, multiple tests of episodic memory, executive functions, and speed of processing are administered. The overall objective is to provide a detailed account of the relationship between losses in DA function and cognitive deficits in aging. Of special interest is to delineate the chain of events from neurotransmission through blood flow to cognitive performance in young and older adults. Of interest is also whether DA losses in certain brain regions (e.g. striatum) are more critical than DA losses in other regions (e.g. frontal cortex) for some age-related cognitive changes (e.g. slower mental tempo), whereas the reverse is true for other cognitive age deficits (e.g. impaired executive functions).