In vivo electrochemistry was used to examine presynaptic alterations in dopamine release in the striatum of aged rats. Chronoamperometric determinations of monoamine release, induced by local micro pressure-ejection of K+, were made using Nafion-coated graphite epoxy electrodes. Recordings were made from the striatum of urethane-anesthetized Fischer 344 rats at 6, 24, and greater than or equal to 29 months of age. Following the in vivo electrochemical experiments, the animals were sacrificed and the caudate nucleus removed for analysis of whole tissue levels of monoamines and their metabolites using standard HPLC techniques. Overall, mean amplitudes of K+-evoked releases from the striatum of 6 month and 24 month F344 rats did not differ significantly (p greater than 0.1). However, this result was complicated by the observation that the mean values obtained from two separate groups of 24 month animals, recorded 6 months apart, were significantly different from each other (p less than 0.001). Mean releases for the later 24 month group were significantly less than for the 6 month group (p less than 0.01). No difference was found in the release magnitudes of 6 month animals recorded contemporaneously with the two groups of 24 month rats. Release amplitudes for the greater than or equal to 29 month group were clearly less than from the 6 month animals (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)