Epsilon is a recently described eye lens protein from Rana temporaria, an anuran amphibian. It is oligomeric with a subunit M.W. of 35K. The cDNA coding for 35Kϵ- in frog lens does not show any homology with cDNA's coding forα,β,γandδ-crystallins. Immunologically, it also does not react with antibodies directed againstα,β-, andγ-crystallins (1).The ontogeny of this 35K E-protein has been investigated in R. temporaria lens development by the indirect immunofluorescence staining method with an antibody specific for the 35K e-protein.The purity of the isolated 35K protein and the specificity of the antibody were controlled by Tris-SDS gel electrophoresis (2) and immuno-blotting, respectively (3).The first positive immunofluorescence reaction was observed in the inner cell wall of a stage V lens. In the external layer/epithelium the reaction was first detected in a single cell of a stage VI1 lens. Additional positive cells in the external layer/epithelium were detected at an early stage Vlll and the reaction appeared to be patchy. This type of patchy reaction was also observed in the epithelium of froglet (sub-adult) eye lens.