The utility of Ca efflux studies to examine lens calcium balance is limited because of the dominant contribution of efflux from the extracellular space of the lens. On the other hand, examination of lens“Ca uptake characteristics can generate valuable information regarding the mechanism by which calcium is largely restricted from the intracellular compartment. Such studies have enabled us to demonstrate that the access of calcium to the intracellular compartment is dependent to some extent upon the concentration of calcium in the extracellular environment. Additionally, experimental evidence speaks against extracellular binding of calcium. Finally, lens membrane permeability to calcium appears to be independent of membrane voltage.