Molecular genetic studies have identified disease-causing mutations at codon 717 of the amyloid protein precursor gene in families with early-onset Alzheimer's disease. Recently, we reported a new mutation at codon 670/671 in a large Swedish family with Alzheimer's disease. The mutation results in two amino acid changes at the N-terminal of the beta-amyloid region. In the present study, we screened for the APP 670/671 mutation in sufferers from 31 other Swedish families with Alzheimer's disease using PCR and restriction enzyme digestion. The mutation was found only in the family previously reported and not in any other family. It is concluded that this mutation is a rare cause of familial Alzheimer's disease in Sweden.