Over the past two years a series of different mutations has been discovered in the amyloid precursor protein (APP) gene in patients with Alzheimer's disease. All have been clustered in exons 16 and 17, a region encoding the beta A4 peptide found in the amyloid deposits of neuritic plaques and cerebral blood vessels. We have used the powerful technique of denaturing gradient gel electrophoresis to screen for mutations in exons 7, 16 and 17 of the APP gene in a cohort of 105 patients with presenile dementia of the Alzheimer type and 71 patients with autopsy-confirmed senile Alzheimer's disease. No new mutations were found, confirming earlier suggestions that APP mutations account for only a small proportion of cases of familial and sporadic Alzheimer's disease.