Antibodies raised against human AChE586-599, reacted to the immunizing peptide and to its cognate BuChE573-586 peptide, but not to the homologous amyloid beta peptide in ELISA. The Western blot detection of three proteins in post-mortem CSF was abolished by competition with AChE586-599,; these proteins were more abundant in AD patient samples. In addition, a-1-antitrypsin (AAT) was found to cause an enhanced signal by specific recruitment of the antibody-peptide complex. This recruitment was more abundant in the AD background, despite equal abundance of AAT in AD and control post-mortem CSF. Oligomeric AChE586-599 was detected in a sandwich ELISA using a single monoclonal antibody. Using this assay, a pos. signal was obtained from healthy hippocampal membranes but not those from an AD background.