Three kinds of missense mutation at codon 717 of amyloid precursor protein (APP) gene (Val --> Ile; Val --> Gly; Val --> Phe) were screened in 114 patients with familial and sporadic Alzheimer's disease (AD), using a rapid testing method for each Val --> Gly and Val --> Phe mutation and Goate's method for Val --> Ile mutation based on the polymerase chain reaction. Mutations were not found in the subjects, confirming earlier suggestions that these three mutations at codon 717 of APP gene account for only a small proportion of cases of not only familial AD but also sporadic AD.