In postmortem brain material of preclinical Parkinson’s disease (PD), clinical PD, and control subjects, we determined with quantitative in situ hybridization and immunocytochemistry the expression of histidine decarboxylase (HDC)-mRNA, the key enzyme of histamine production, and the amount of Lewy bodies/Lewy neuritis (LBs/LNs), the pathology markers of PD, in the hypothalamic tuberomammillary nucleus (TMN). No significant difference of HDC-mRNA levels was observed either in the preclinical or in the clinical PD patients, in spite of the strong accumulation of LBs/LNs in the TMN of clinical PD. These findings indicated that the neuronal histamine production remains largely unaltered in PD, and that the pathological alteration of PD may rather protect the TMN from degeneration instead of causing degeneration. This study provides new ideas for studying PD pathogenesis. The paper was published in Neurobiology of Aging.