The presenilin-1 (PS-1) gene was recently identified as one of the causative genes in the early onset of familial Alzheimer's disease (AD). Analysis of the PS-1 gene is thought to be useful in clarifying the pathogenesis of AD. However, there have been few reports about the expression of the PS-1 gene in AD. In this study, we analyzed the expression of PS-1 mRNA in cultured skin fibroblasts taken from living patients with AD by Northern blot analysis. The subjects consisted of 18 cases with AD and 10 cases of neurological patients without dementia (CTL). We found that the PS-1 mRNA levels in AD were significantly higher than those in CTL (p < 0.01). Moreover, we found that the PS-1 mRNA level increases in the early stages of AD and tends to decrease in the advanced stages. These findings suggest that high levels of PS-1 mRNA may play an important role in developing AD.