By means of liver-absorbed rabbit anti-adult rat lens sera, and by using the indirect immunoperoxidase technique, lens-specific antigens are detectable in a few isolated cells, or in small groups of cells, of the placode shortly after the onset of invagination. In the deeply invaginated lens rudiment, all the cells, exept those in the area adjacent to the ectoderm (presumptive lens epithelial cells) display a positive reaction. Once the lens vesicle has formed, all the cells contain detectable amounts of lens-specific antigens.