The human beta-amyloid protein is deposited in senile plaques and in the cerebro-vasculature of people with Alzheimer's disease and Down's syndrome. The precise role of beta-amyloid in Alzheimer's disease pathology is presently unknown. To study the properties of beta-amyloid in vivo, we generated transgenic mice that harbor the gene for the carboxyl-terminal 100 amino acids of the human amyloid precursor protein, beginning with the beta-amyloid region, under control of the JC viral early region promoter. The mRNA is expressed exclusively in brain tissue. Further, we demonstrate increased levels of beta-amyloid immunoreactivity on fixed brain tissue. These animals will be useful as a model to study beta-amyloid deposition and its consequences.