Epidemiological studies implicate estrogen deprivation as a risk factor for Alzheimer's disease and postmenopausal estrogen replacement as protective factor. One potential mechanism involves estrogen attenuation of β-amyloid (Aβ) peptide accumulation. We examined the effect of estrogen on amyloid accumulation in female PDAPP mice, which express human amyloid precursor protein (APP) with the V717F mutation. These animals deposit Aβ 1-42 in the hippocampus and neocortex amd develop Alzheimer-like neuropathology. Mice were subjected to ovariectomy, ovariectomy with estrogen replacement, or sham surgery at 3 months of age, and levels of cerebral Aβ 1-40 and 1-42 were determined after 5 months of treatment. Neither estrogen deprivation nor estrogen replacement altered Aβ accumulation in the hippocampus or neocortex. Similarly, immunoreactivity for full-length human APP and secreted APPα was unchanged. Estrogen status of the animals was confirmed using a variety of techniques, including uterine and pituitary weight, vaginal cytology, and plasma estradiol concentrations. There was no correlation between plasma estradiol levels and accumulation of either Aβ 1-40 or Aβ 1-42 in the brain. Our observations indicate that long-term estrogen therapy does not alter amyloid pathology in PDAPP mice, an animal model of Alzheimer's disease, and question the role of estrogen in Aβ deposition in brain.