The contribution of the duration of the striatal dopamine (DA) depletion and the expression of parkinsonian signs to changes in D(1) and D(2) receptor number was investigated in the present study. Some animals (N=4) received large doses of 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP) over short periods of time and were symptomatic for a short period of time (1-3 months; acute parkinsonian group). Other animals (N8 months; chronic parkinsonian group). Despite similar symptomatology and similar degrees of striatal DA denervation, only acute parkinsonian animals had significantly increased numbers of D(1) receptors in most striatal regions. Striatal D(2) receptor binding was elevated in acute parkinsonian monkeys but only in some lateral striatal subregions at mid and caudal levels. These findings further suggest that the duration of parkinsonism is a critical factor in modulating changes in striatal neurochemistry.