Cu, Zn superoxide dismutase (SOD) levels in the serum, cerebrospinal fluid (CSF) and skin fibroblasts of patients with dementia of the Alzheimer type (DAT) were estimated using enzyme immunoassay. The SOD mRNA level in the skin fibroblasts was also determined by the Northern blot analysis. As compared with the age-matched control groups of neurological patients without dementia, the AD group consisting of patients with DAT at ages under 65 years of age as well as the SDAT group of patients with DAT at ages over 65 years of age showed no significant changes in serum or CSF SOD levels. However, the skin fibroblast SOD- and SOD mRNA levels, which were correlate each other, were significantly higher in the AD group (p<0.05), while lower in the SDAT group (p<0.05). These results suggest that the determination of the SOD level of skin fibroblast may be useful for diagnosis of DAT and that the abnormality of SOD may play an important role in developing DAT.