The neurotoxin MPP + potently inhibited the striatal binding of [ 3H]-tyramine, a putative marker for the vesicular transporter of dopamine, and provoked a massive in vivo release of striatal dopamine. Tetrabenazine, an established ligand for the vesicular catecholamine carrier, potently inhibited [ 3H]-tyramine binding, tyramine-provoked striatal efflux of dopamine and the fast component of MPP +-induced dopamine release. It is concluded that MPP + in the striatum, besides interacting with additional intracellular targets, avidly binds at a vesicular site functionally involved with the outward transport of dopamine.