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Forty-five patients presenting a parkinsonian syndrome, accompanied in some cases by depressive and/or confusional signs, were subjected to neurological and neurobiochemical investigation involving a probenecid test (estimate of central turnover of dopamine by determination of homovanillic acid in cerebrospinal fluid before and after an oral dose of probenecid). Patients were classified in two groups on the basis of the benefit procured by dopa therapy as estimated at least one year after treatment. The probenecid test revealed a sharp drop in turnover of dopamine in the dopasensitive group. Furthermore, in this group the dopamine turnover was not related to sex, age, duration of the parkinsonian syndrome or clinical severity. In contrast, there seemed to be a correlation between dopamine turnover and optimum dosage of l-DOPA. Lastly, the study showed that, beyond the diagnosis of dopasensitivity, the test was useful for patient follow-up. The test profile in cases of excess dopatherapy is described.