Data on superoxide dismutase (SOD) activity in the cerebrospinal fluid (CSF) of patients suffering from dementia (n=32) as compared with a control group (n=58), a Parkinson disease (PD) patient group (n=12), and a group of individuals suffering from epilepsy (n=13) are presented. SOD activity was determined by electron spin resonance spectrometry using the spin trap method. No significant correlation was found between CSF SOD activity and age in the control group. In addition, CSF SOD activity was not gender dependent. One-way analysis of variance showed a highly significant between-groups effect for the CSF SOD activity and specific CSF SOD activity of the four major groups (p=0.0008). Post hoc comparison (Fisher PLSD test) revealed significant differences between the control group and the total dementia group (p < 0.001), between the dementia group and the epilepsy group (p < 0.01), and between the dementia group and the PD group (p < 0.05). The CSF of patients with PD or epilepsy showed a similar SOD activity as the CSF of control patients. In addition, CSF SOD activity levels were significantly lower in the total dementia group (p=0.002) and in the group with dementia of the Alzheimer type (DAT) (p=0.001) than in the dementia age-matched control group. No significant difference was found for CSF SOD activity levels between the control group and the non-DAT dementia group. This result corresponded with a reduction of CSF SOD activity in the total dementia group, DAT subgroup, and non-DAT subgroup of 37, 43, and 22%, respectively. No significant correlation between the Mini-Mental State Examination score and CSF SOD activity was found in DAT. The lowered CSF SOD activity in Alzheimer disease, as demonstrated here, may reflect impaired radical defense mechanisms and may have possible pathophysiological significance.