In cerebrospinal fluid, levels of the histamine metabolites, tele-methylhistamine and tele-methylimidazole-acetic acid, were higher in elderly than in young people, and women had higher levels than men. Therefore, age and gender should be considered in studies of histamine metabolites as exemplified by their measurements in cerebrospinal fluid of patients with Huntington's disease. Levels of pros-methylimidazoleacetic acid, an isomer of tele-methylimidazoleacetic acid and not a metabolite of histamine, were higher in cerebrospinal fluid of men than of women. Levels of pros-methylimidazoleacetic acid in cerebrospinal fluid were highly positively correlated with the severity of Parkinson's disease in a group of non-medicated, mildly to moderately affected patients.