AIM: To analyze and identify the proteomic differences between liquefied after-cataracts and normal lenses by means of liquefied chromatography-tandem mass spectrometry (LC-MS/MS). METHODS: Three normal lenses and three liquefied after-cataracts were exposed to depolymerizing reagents to extract the total proteins. Protein concentrations were separated using two-dimensional gel electrophoresis (2-DE). The digitized images obtained with a GS-800 scanner were then analyzed with PDQuest7.0 software to detect the differentially-expressed protein spots. These protein spots were cut from the gel using a proteome work spot cutter and subjected to in-gel digestion with trypsin. The digested peptide separation was conducted by LC-MS/MS. RESULTS: The 2-DE maps showed that lens proteins were in a pH range of 3-10 with a relative molecular weight of 21-70 kD. The relative molecular weight of the more abundant proteins was localized at 25-50 kD, and the isoelectric points were found to lie between PI 4-9. The maps also showed that the protein level within the liquefied after-cataracts was at 29 points and significantly lower than in normal lenses. The 29 points were identified by LC-MS/MS, and ten of these proteins were identified by mass spectrometry and database queries: beta-crystallin B1, glyceraldehyde-3-phosphate dehydrogenase, carbonyl reductase (NADPH) 1, cDNA FLJ55253, gamma-crystallin D, GAS2-like protein 3, sorbitol dehydrogenase, DNA FLJ60282, phosphoglycerate kinase, and filensin. CONCLUSION: The level of the ten proteins may play an important role in the development of liquefied after-cataracts.