High-resolution images of cholesterol were obtained from Lymnaea stagnalis nervous tissue using metal-assisted (MetA) time-of-flight secondary ion mass spectrometry (ToF-SIMS). The spatial distributions of different pseudomolecular ions of cholesterol [M - H](+), [M -OH](+) and [2M + Au](+), illustrate the influence of the tissue microenvironment on the ionization efficiencies of these ions. These biological matrix effects result in differences in localizations of molecular ions derived from the same molecular species. (c) 2006 Elsevier B.V. All rights reserved.