Résumé : After describing the clinical picture of parkinsonism, other Parkinson and depressive syndromes, the authors clarify ascending dopaminergic and serotoninergic pathways in the central nervous system as well as current knowledge on the nigrostriatal pathway. They also underline the interest of the probenecid test in the diagnosis of parkinsonism with or without depression. Neurochemical criteria of dopa-sensitivity and dopa-resistance are proposed as well as criteria aimed at serotoninergic therapy. Finally, the use of this neurochemical test in treatment and follow-up is illustrated by a clinical case report.