Soemmerring's ring is one form of "after cataract" that can occur following cataract surgery. The ring structure is formed by adherence of the anterior lens capsule to the posterior lens capsule. Epithelial cells remaining after surgery differentiate into lens fiber cells but the resulting tissue mass does not remain transparent. The protein in normal lens and in Soemmerring's rings from four individuals was analyzed using two-dimensional (2-D) gel electrophoresis, matrix assisted laser desorption/ionization-time of-flight-mass spectrometry (MALDI-TOF-MS) and image analysis with Phoretix software. The 2-D protein patterns of the Soemmerring's rings were generally similar to that of cortical fiber cells of normal human lens with some notable exceptions. Several posttranslationally modified forms of alpha beta-crystallin((1-175)) were identified. Two degradation products, alpha beta-crystallin((1-170)) and alpha beta-crystallin((1-174)), each make up 9.5-27% of the total alpha beta-crystallin in the Soemmerring's rings and less than 1% in the normal lenses. Other modified forms of alpha beta-crystallin are aberrant in the fiber cells of the Soemmerring rings relative to normal lens.