Changes in wet weight, dry weight and water content have been studied in different types of senile cataract and compared With transparent control lenses. While nuclear brunescent cataractous lens show normal weight, protein and water content, cortical opacification is characterized by a progressive decrease of total lens proteins associated with important terminal alterations of the percentage of water content. Posterior subcapsular cataracts in very early stages of the disease have a significantly lower wet weight than control lenses, but a normal protein-water ratio; this is interpreted as a decreased lens growth starting far back in time and producing apparently normal lens substance. The question is raised whether this could be interpreted as a manifestation of the same pathogenetic cause which determines the appearance of this type of lens opacification.