The patterns of amyloid β (Aβ) peptides in human cerebrospinal fluid (CSF) and brain homogenates were studied by surface-enhanced laser desorption/ionization (SELDI) time-of-flight (TOF) mass spectrometry, and the results were compared with those obtained by Aβ-SDS-PAGE/immunoblot. Apart from the peptides known in the literature to occur in the CSF, we postulate the existence of a novel, previously not described peptide, either Aβ1–45 or Aβ2–46. This peptide was observed exclusively in a pool of samples originating from patients with AD, i.e. CSF and postmortem brain homogenates, but not in either the pooled CSF samples nor the pooled brain homogenates of the non-demented controls. Similarly to our previous results, Aβ1–42 was decreased in the CSF in AD. Expectedly, brain homogenates of the control subjects did not show the presence of Aβ peptides. Compared with Aβ-SDS-PAGE/immunoblot, SELDI-TOF enabled more precise analysis of Aβ peptides in the human material. We conclude that SELDI-TOF offers a promising tool for dementia expression pattern profiling using a minute amount of a biological sample. Copyright © 2003 John Wiley & Sons, Ltd.