Traumatic cataract was induced in rats and rabbits. The progression of the posterior subcapsular cataract and wound healing were followed by quantitative microradiography to determine the dry mass content and refractive indices in the lens. In the injured rat lens, a reduced dry mass concentration occurred in the wound region and posterior subcapsular region immediately after trauma. During the 1st wk a subcapsular opacity enlarged. Opacification always corresponded to a reduction in the subcapsular concentration of dry mass. The reduced content of dry material, consisting mainly of protein, was apparently a hydration of the subcapsular cortex. In the rabbit lens, a much larger injury was needed to cause any posterior cataract. The same reduction in dry material was determined in regions corresponding to opacities. The reduction was more pronounced in the rat lens. The border zones between different concentrations of dry mass were apparently the main sources of scattered light in the traumatic cataract.