Presenilin-1 (PS-1) was suggested to be localized on 14q24.3 based on linkage analysis and cDNA cloning. The final identification of PS-1 as the causal gene for Alzheimer's disease (AD) was concluded based on finding of the point mutations in the candidate cDNA linked with pedigrees with early-onset familial AD. We present evidence of its physical genome mapping of PS-1 by fluorescence in situ hybridization method.