X-irradiation of frog eyes with natural and experimentally induced differences in lenticular mitotic activity reveals cataractogenesis to be dependent on the proliferative activity of the germinative zone of the lens epithelium. It has also been found that G₀ cells are sufficiently vulnerable to X-rays to cause opacity if cell division is allowed to occur following irradiation. In every case of X-ray-induced lens opacification, a disruption of the radiating columns shows a strong correlation to the severity of the associated cataract. It is suggested that lens cell damage from ionizing radiation is transduced by mitosis and expressed as an opacity by subsequent errant fiber genesis.