Distribution of ions and volume regulation of epithelial cells of lenses cultured in the presence and absence of vitreous humor were examined. Ion levels of the epithelial cells were measured using energy dispersive x-ray analysis(EDX) and computer-assisted morphometry was used for volume measurements. Data from these experiments revealed that the epithelial cells in the pre-equatorial region of lenses cultured without attached vitreous humor are larger and have significantly altered ionic balance. The cell volumes and ionic balances of central epithelial cells of the lenses cultured without attached vitreous humor also displayed discernible changes. However, overall data indicated that the epithelial cells in the pre-equatorial regions of the lenses are most susceptible to the effects of vitreous humor. Experiments performed in our laboratory have demonstrated that vitreous humor contains some factor(s) which can effectively inhibit protein synthesis. It was also reported that this factor(s) is not a direct inhibitor of protein synthesis. Therefore it was assumed that the inhibition of protein synthetic activity was mediated via some other pathway. One of these possible routes could be altered cytoplasmic ion fluxes. Earlier we reported that the ion levels of the lenses cultured with or without adhered vitreous humor were similar. Ion levels were measured from intact lenses. It is possible that there were regional differences in ion levels, which could be masked in whole lenses. It is also known that the epithelial cells are major participant in ion-pump activity, whereas cortical and nuclear areas of the lens may not contribute significantly to the ion transport. It has also been proposed that the epithelial cells of the pre-equatorial region are the main site of the Na+, K+ pump. Variation in ion levels of the epithelial cells could also affect protein synthesis activities of the lens. To test these possibilities, experiments were performed to measure ion levels in various areas of the lenses by energy dispersive x-ray analysis techniques. Altered cytoplasmic ion level can also change the volumes of the epithelial cells. This possibility was investigated by employing computer-assisted morphometry in measurements of two- and three-dimensional parameters of the lens epithelial cells and capsule.