The effects of age on dopamine (DA) release in the nucleus accumbens (NAc) and on amphetamine (AMPH)-induced locomotor activity were studied by microdialysis in freely-moving young (5 month) and old (24 month) rats. Both basal extracellular DA and 3,4-dihydroxyphenylacetic acid (DOPAC) release and that following intra-accumbens perfusion of AMPH (1-10 microM) were significantly lower in old rats. After intraperitoneal injection of AMPH (1.5 mg/kg), no age-related change in DA release was seen in the NAc, but locomotor activity was found to increase much more in young rats than in old ones. These results indicate that (1) old rats show decreased extracellular DA and DOPAC release, both in the basal state and following intra-accumbens infusion of AMPH, and (2) the age-related locomotor activity induced by systemic injection of AMPH is not paralleled by changes in DA release in the NAc.