Mutations in the presenilin-1 gene (PS-1) on chromosome 14 are causative for early-onset familial Alzheimer's disease (AD). In order to study the localization of PS-1 in human brain, a polyclonal antibody, SB63, against a N-terminal epitope of PS-1 (25VRSQNDNRERQEHND40), was raised in rabbits and characterized. Immunolabeling with SB63 of formalin-fixed sections of hippocampus from cases of PS-1-linked AD (PS-1 I143T (AD/A), G384A (AD/B)), sporadic AD, and controls showed a predominant neuronal staining pattern with a stronger immunoreactivity in pyramidal neurons. Staining was mainly granular and localized in the neuronal cell body as well as in neuronal processes. In AD some dystrophic neurites surrounding the amyloid plaques were stained, but no immunoreactivity was observed in the amyloid core. Although PS-1 was present in tangle bearing neurons, colocalization of PS-1 and tau could not be detected using immunofluorescence double labeling. Our data indicate that the pattern of PS-1 immunoreactivity in the hippocampus does not substantially differ between PS-1-linked AD, sporadic AD, and controls.