Low concentrations of D-amphetamine (AMPH) released [3H]dopamine (DA) from purified, rat brain synaptic vesicles with exponential kinetics and a half-time of 4 min. Slight alkalinization of the vesicles by AMPH seemed unable to account for this release. Instead, it is likely that AMPH partially inhibits DA uptake after which DA escapes by an uptake-independent pathway. At high concentrations the proton gradient was severely reduced by AMPH and DA was released with a half-time of < 1 min. Loss of the proton gradient was sufficient to account for this DA release. These results show that low concentrations of AMPH release DA from synaptic vesicles and suggest that release occurs by different mechanisms at low and high AMPH concentrations.