Studies were conducted on the development of cataract in the eyes of young (5-6 week old) New Zealand White rabbits exposed to 20 Gy of X-rays (1 Gy = 100 rads). The findings indicated that the opacities appear initially during the first week post-irradiation and follow a progression typical of cataract development in older rabbits and other species. However, advanced cataractous changes, as indicated by lens intumescence, occur concomitantly with complete opacification. They develop rapidly within a two day period between 2.5 to 3 months post-irradiation.