Lens changes caused by injury to the anterior part of the lens were studied with Procion yellow as an extracellular tracer and by transmission electron microscopy at different time intervals after trauma. Both rats and rabbits were used. The findings were related to the slit-lamp appearance of the wounded lenses. In the rat lens a posterior subcapsular cataract developed within the first hour after trauma. Within 1 hr after injury the fluorescent tracer was seen at the wound but was also conspicuous at the posterior pole. Swelling of lens fiber cells and the formation of large syncytical aggregates were found as the posterior opacity enlarged. These changes reached the anterior subcapsular cortex via the equatorial cortex after about 1 month. In the rabbit lens a slight cellular swelling was seen in the subcapsular cortex. Only in one of 15 lenses a posterior subcapsular opacity developed after about 1 week in spite of a large wound. The uptake of Procion yellow was most prominent in the wound area and was never observed at the posterior pole. In both species, no further penetration of the dye occurred through the wound after the epithelium, by regeneration, had sealed the wound. The importance of epithelial wound sealing and that of a restored cellular barrier at the posterior pole are discussed as well as the significance of these factors in the cataract progression.