The purpose of this experiment was to test the effectiveness of E64 in prevention of selenite nuclear cataract in the whole animal. E64 is an inhibitor of cysteine proteases such as calpain (EC.3.4.22.17). In the whole animal, daily intraperitoneal injection of E64 was mildly effective in slowing the rate of formation of selenite nuclear cataract, although prevention was not permanent. Frequency of the nuclear cataract in selenite group at 5 days post selenite injection was significantly decreased from 40% to 17% in the selenite+E64 group, and the density of cataract in the Se+E64 group was reduced. However, crystallins and calpain were still degraded in the selenite+E64 group. E64 was more effective against selenite cataract when present continuously during lens culture, where it slowed the rate of formation of nuclear opacity. Amelioration of cataract occurred bothin vitroandin vivoeven though lens calcium concentrations were elevated. The results supported the idea that application of calpain inhibitor is beneficial hi prevention of rodent selenite cataracts.