Monkeys were treated on two regimens of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injections to achieve dopamine fiber degeneration of differing severities. A rapid treatment regimen produced a severe parkinsonian syndrome, whereas an intermittent regimen did not cause locomotor symptoms to appear up to 25 weeks. High resolution PET scanning of dopamine nerve terminals revealed that the specific binding of the dopamine transporter [11C]-WIN 35,428 ([11C]-CFT) was diminished by 94% (caudate nucleus) and by 93% (putamen) in the symptomatic monkey. Decreases of 65 and 67% were detected in these regions in the non-symptomatic monkey. Post-mortem immunocytochemical evaluation of presumed dopamine fibers by tyrosine-hydroxylase showed similar reductions in the symptomatic animal.