We have developed a capable tool for visualizing protein distribution at the sub-cell level with TOF-SIMS. This new method of visualizing a protein includes: (1) printing a digestive enzyme with ink jet (IJ) printing technology onto a tissue section, (2) measuring the two-dimensional distributions of decomposed peptide ions derived from digested protein on the tissue section by TOF-SIMS with a bismuth cluster ion (Bi-3(+)) source and using the aqueous ion enhancement method, and (3) analyzing the two-dimensional distributions of proteins using the results of proteome analysis. We have not yet tried this method onto a real tissue section. To show the possibility of this method, TOF-SIMS results of visualizing dot-patterned digested fragment peptide ions using IJ printing digestion technique onto a protein film are presented. (c) 2008 Elsevier B.V. All rights reserved.