Soluble amyloid-beta (A beta) oligomers are thought to be a cause of neurodegeneration and memory loss in Alzheimer disease (AD). We recently reported a newly developed enzyme linked immunosorbent assay (ELISA) for high molecular weight (HMW) A beta oligomers in which the same A beta monoclonal antibody, BAN50, was used for both capture and detection in a single antibody sandwich ELISA (SAS-ELISA) system. Our previous data suggest that this assay will be useful for the early diagnosis of AD, but its practical application to large-scale or longitudinal studies has been limited because of lack of a reliable calibration standard. In order to develop such a standard, we have now constructed a novel peptide using the multiple antigenic peptide (MAP) technique, where multiple epitopes of BAN50 were linked, via a spacer, to a branching lysine core. We show that the standard curve constructed from a 16-mer MAP covered the physiological range of signals obtained in the BAN50 SAS-ELISA from samples of human CSF, serum, and plasma. Furthermore, this 16-mer MAP is available in large quantities and is stable against freeze-thawing. We estimate that the signal per 1 pM of this standard corresponds to 1.54-5.0 pM of HMW A beta oligomers. This MAP approach could also be used to provide an effective calibration standard for other SAS-ELISAs. (c) 2012 Elsevier Inc. All rights reserved.