AbstractNine groups of experiments on 537 eyes of adult newts,Triturus v. viridescens, examined conditions under which lens regeneration is inhibited or released from dorsal iris tissue. The lens is quite vulnerable for it degenerates when the lens capsule is injured and when the neural retina degenerates following a temporary loss of blood supply. Degeneration of neural retina in lentectomized eyes delays lens regeneration from both implanted and host dorsal iris. If degeneration of neural retina is induced after lens regeneration begins its further development is temporarily retarded until the neural retina proceeds to regenerate.If one of two large lens regenerates in a single eye is removed, one from the host eye or one from an implanted segment of dorsal iris, the surviving lens inhibits further lens regeneration from any dorsal iris tissue present. Two dorsal halves of eyes can be fused into one normal appearing unit which regenerates two lenses, one from each half. When one lens is removed the remaining lens inhibits lens regeneration from either half in the environment of a normal amount of neural retina.If a plastic membrane is implanted to divide the upper and lower halves of the eye into two separate chambers, each with its own aqueous humor and half of the neural retina, lens regeneration from the isolated iris above is no longer inhibited by the intact normal lens below.