Recent reports suggest an association between an intronic polymorphism at the 3' position of exon 8 of the presenilin-1 (PS-1) gene and late-onset Alzheimer's disease (AD), but little is known about its role in the pathogenesis of AD. By genotyping 193 Japanese patients with vascular dementia or AD, and 186 elderly control subjects, we have shown no association between vascular dementia and this PS-1 polymorphism, though PS-1 genotype 1/1 and allele 1 frequencies were both significantly higher among patients with AD than among controls. These results argue for a specific role of PS-1 allele 1 in the pathogenesis of AD, rather than suggesting a broader role for this allele as, for example, in vascular dementia.