The contribution of striatal (caudate nucleus-putamen) dopaminergic deficiency to the severity of motor signs is well established in Parkinson's disease (PD), while its role in the occurrence of cognitive and mood changes remains unresolved. We therefore measured in 27 non-demented PD patients and 10 age-matched controls striatal uptake of [18F]-6-fluoro-L-Dopa (F-Dopa) with PET, and mood (Beck depression), memory (Grober-Buschke), frontal executive functions (verbal fluency and Wisconsin card sorting), and attentional processing of sensory stimuli (N2-P3 auditory event-related potentials--ERPs). Locomotor disability of patients was assessed by Hoehn and Yahr score and Unified Parkinson's Disease Rating Scale (UPDRS). ANOVA showed that memory, but neither frontal lobe functions nor ERPs, was significantly altered in PD patients, whereas indices of depression were found only in advanced PD. The F-Dopa rate constant Ki was significantly reduced in the striatum, more in putamen than caudate nucleus, and inversely correlated with disease duration. A significant inverse correlation was found between both putamen and caudate nucleus Ki and Hoehn and Yahr score, and between putamen--but not caudate nucleus Ki --and UPDRS motor score. Principal components analysis (PCA) of PD patients Ki values and mood, cognitive and ERP parameters gave a three-factor solution. Variables contributing to factor 1 were memory score and N2-P3 ERP latencies, those to factor 2 were striatal Ki values, and those to factor 3 frontal executive performances. Depression did not segregate with any variable. Our findings suggest that unlike locomotor disability, cognitive abilities and mood state of non-demented PD patients are for the most part unrelated to striatal dopaminergic depletion and may result from dysfunction of extra-striatal dopaminergic or from non-dopaminergic systems.