We examined IL-6 levels in the cerebrospinal fluid (CSF) of patients clinically diagnosed with Alzheimer-type dementia (ATD) and with vascular dementia (VD) and of age-matched normal subjects. The IL-6 levels in the CSF of ATD, but not VD patients, were significantly decreased. In the early onset ATD patients (disease onset < 65 years), IL-6 levels were reduced to 21% of the control level. The IL-6 levels in the CSF were not associated with the severity of the dementia or the duration of the disease since the identification of the first symptoms.