The catecholamine precursor l‐3,4‐dihydroxyphenylalanine (l‐DOPA) is used to augment striatal dopamine (DA), although its mechanism of altering neurotransmission is not well understood. We observed the effects of l‐DOPA on catecholamine release in ventral midbrain neuron and PC12 pheochromocytoma cell line cultures. In ventral midbrain neuron cultures exposed to 40 mM potassium‐containing media, l‐DOPA (100 µM for 1 h) increased DA release by >10‐fold. The elevated extracellular DA levels were not significantly blocked by the DA/norepinephrine transport inhibitor nomifensine, demonstrating that reverse transport through catecholamine‐uptake carriers plays little role in this release. In PC12 cells, where DA release from individual secretory vesicles can be observed, l‐DOPA (50 µM for 1 h) elevated DA release in high‐potassium media by 370%. Amperometric measurements demonstrated that l‐DOPA (50 µM for 40–70 min) did not raise the frequency of vesicular exocytosis but increased the average size of quantal release to at least 250% of control levels. Together, these findings suggest that l‐DOPA can increase stimulation‐dependent transmitter release from DA cells by augmenting cytosolic neurotransmitter, leading to increased quantal size.