A tumor-like growth in the lens of Rana pipiens occurs following mechanical injury to the lens. The frequency of occurrence and size of the growth are roughly dependent on the extent of the injury inflicted. The growth first appears four days after wounding, grows actively for three weeks and usually begins to regress after a month. The cells of the growth appear to originate by proliferation of the lens epithelialcells surrounding the wound which grow into and actively invade the lens fibers. The lens growth was not transplantable either homologously into the anterior eye chamber after dissociation, nor isologously in a subcutaneous site. Protein, LDH, MDH, and G-6-PD patterns obtained after electrophoretic separation in starch gels were similar for normal and the abnormal lenses. Whether a true tumor or hyperplasia, the froglens exhibits an unique reaction to the injury stimulus which is not found in mammals (man, rabbit, mouse). The controversial tumor immunity of the mammalian lens appears to the related to an innate resistance of the epithelium to proliferation which is illustrated in part by the species difference in the reactivity of the mammalian lensand the amphibian lens to injury.