p75(NTR), a low-affinity neurotrophin receptor, may be involved in the pathogenesis of Alzheimer's disease (AD). The aim of present study was to detect the relationship between p75(NTR)-containing neurons and the pretangles consisting of hyperphosphorylated tau stained by Alz-50 in the hippocampus of AD patients. Samples of hippocampus of 10 female AD patients and 10 nondemented female controls matched for age and postmortem delay were investigated immunocytochemically, and the stainings were quantified using an image analysis system. The results showed that: (i) p75(NTR) was present in about half of the pyramidal neurons of the CA1-CA4 subfields of hippocampus. No difference was observed in the number of p75(NTR) immunoreactive neurons in the CA1-CA4 subfields between the two groups. Interestingly, the ratio of p75(NTR) expressing neurons to the total number of neurons as staining with thionin was significantly higher in the CA1 and CA2 subfields of AD hippocampus than in controls. (ii) There were a large number of Alz-50 neurons and double-labeled neurons containing p75(NTR) and Alz-50 in the CA1 and CA2 subfields of AD patients. These results suggest that p75(NTR) may be involved in the formation of tangles in the Alzheimer process.