Two-dimensional polyacrylamide gel electrophoresis (2-DE) profiles of human lung squamous carcinoma tissue and paired surrounding normal bronchial epithelial tissue were compared. Selected differential protein-spots were identified with peptide mass fingerprinting based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and database searching. Well-resolved and reproducible 2-DE patterns of both the tumor and the normal tissues were acquired. The average deviations of spot position were 0.873 0.125mm in IEF direction and 1.025 0.213mm in SDS–PAGE direction, respectively. For the tumor tissues, a total of 1349 67 spots were detected and 1235 48 spots were matched with an average matching rate of 91.5%. For the corresponding normal tissues, a total of 1297 73 spots were detected and 1183 56 spots were matched with an average matching rate of 91.2%. A total of 1069 45 spots were matched between the tumor and the normal tissues. Forty differential proteins between tumor and normal tissues were characterized. Some proteins were the products of oncogenes and others were involved in the regulation of cell cycle and signal transduction. These data are valuable for mass identification of differentially expressed proteins involved in lung carcinogenesis, establishing human lung cancer proteome databaseand screening molecular marker to further study human lung squamous carcinoma.2003 Published by Elsevier Inc.