The application of molecular genetic techniques to the study of autosomal dominantly inherited Familial Alzheimer's Disease may provide a means to determine the chromosomal location of the defective gene causing this form of Alzheimer's disease. Knowledge of the chromosomal location of the defective gene will provide a basis for isolating and characterizing this gene. Preliminary investigations indicate that several candidate genes can be excluded as the site of the defect. Current data also indicate that the defective gene does not reside close to random DNA markers on the distal portion of chromosome 21. Additional DNA markers on the proximal portion of chromosome 21 long arm are currently being investigated.