Abstract [ 18 F]-6- Fluoro-β- fluoromethylene-m- tyrosine ([ 18F]FFMMT) was evaluated as a potential imaging agent for dopamine nerve terminals using positron emission tomography (PET). Biodistribution and time course of this tracer in mice after i.p. injection was consistent with the distribution of dopamine. PET imaging studies involving rhesus macaques showed specific uptake in the dopamine-rich caudate-putamen region. This specific localization was blocked by inhibiting the enzyme l-aromatic amino acid decarboxylase and the transport of the tracer into brain was shown to be stereospecific. These results show the promise of l-[ 18F]FFMMT as a PET tracer in monitoring degeneration of the CNS dopamine system.