Calcium is an important factor in many cellular activities and in the maintenance of structural integrity of membranes. Calcium accumulation in the rat lens above the normal physiological range (0.11 µmol/g wet weight) has been associated with formation of cataracts. Selenite is known to influence the histological characteristics of the lens and also alter important biochemical functions. In the selenite induced cataract calcium levels increase as much as 5-fold above normal, the increase preceding appearance of mature opacity by 24 hours. Calcium in the lens rapidly exchanges with labelled calcium in the incubation medium and. establishes equilibrium within 30 minutes. Selenite, accumulated in lens in vivo, causes a 5-6 fold increase in lens calcium over controls during a 24 hour incubation in modified Hank's medium at 37°C. In vitro lmM selenite in the culture medium results in a 15-fold increase in lens calcium, a 17-fold increase in sodium/potassium ratio, and a 60% increase in lens hydration. Efflux of calcium from in vivo and in vitro selenite-treated lens is not impaired. The lens retains the capability to transport 3-4 fold greater calcium over controls from lenses which have accumulated excess calcium in the presence of selenite. In vivo selenite treatment results in a 2.5-fold increase only of extracellular water. In in vitro selenite-treated lenses, however, there is a 2.6-fold increase in extracellular water and a 1.8-fold increase of intracellular water. Selenite treatment of the lenses in vivo and in vitro causes a greater influx of calcium into the lens. Calcium accumulation may act in a nonspecific manner altering lens biochemical functions, membranes and structure, causing development of relationships between selenite induced lens fiber opacities. cataract and cell the associated changes in lens calcium content further validates this model for studying the biochemical changes which impact cataract formation. / Master of Science