Earlier experiments demonstrated that mitosis in the lens epithelium of anura is controlled by pituitary and thyroidal hormones. These hormones seem to achieve their effect by production of somatomedin-like substance. Recent work implies that the liver may be the site of production of the relevant mitogen. Initial studies suggest that the liver undergoes histological and cytoarchitectural changes in the absence of the pituitary and these changes need to be explained. We will, therefore, study the structure of the liver of hypophysectomized animals and hypophysectomized animals that have received replacement therapy with human growth hormone. The serological changes that occur in such organisms will also be documented. The mode of action of somatomedin-like substances on organ cultured lenses will be explored and we wish to determine if the cartilage of amphibia can be used as a gauge of somatomedin activity in a fashion similar to that used with mammals. Additional studies on the generation of radiation cataract in hypophysectomized animals will be pursued as will the culture of the amphibian lens epithelial cells. Possible effects of hypophysectomy on the growth properties of ocular tissues other than lens epithelium will be sought.