Proteins corresponding to growth hormone and prolactin were electrophoretically separated from the pituitary gland of the frog (Rana pipiens berlandieri and R. catesbeiana). These substances can independently stimulate mitosis in the lenses of animals where it had previously been inhibited by means of hypophysectomy. DNA synthesis is greatly augmented 6 days after the start of hormone administration to intact animals. Nine days are required before this occurs in hypophysectomized ones. No other anterior pituitary hormone achieved the effect. Initial attempts at amino acid analysis, though incomplete, indicate that the 2 frog hormones are different from each other and from their bovine counterparts. Pituitary factors do not affect mitotic activity in either corneal epi- or endothelium of the frog.