The relationship between dopamine receptor activation and the relief of parkinsonian clinical features was studied in 40 patients with Parkinson's disease. Treatment with dopamine receptor agonists, piribedil or bromocriptine, decreased significantly both the basal level and probenecid-induced accumulations of homovanillic acid (HVA) in the CSF. But there were no changes in the concentrations of 5-hydroxyindole acetic acid (5-HIAA). Correlation analyses showed that patients who improved with both the dopamine agonists used had significantly lower probenecid response of HVA in the CSF and a less severe disease condition than those without beneficial effect. This relationship between dopamine receptor activation and improvement of parkinsonian disability suggests that the therapeutic efficacy of dopamine receptor agonists depends on the functional capacity of brain dopaminergic mechanisms.