The specific aims are to study the mechanisms of pituitary growth and differentiation by (1) analyzing cytodifferentiation in the adenohypophysis in dwarf (dw) and little (lit) mutant mice, (2) examining cellular kinetics in the postnatal glands of normal mice, and (3) comparing and analyzing tissue interactions among the adenohypophysis, neurohypophysis, and brain in mouse and rhesus monkey embryos. A variety of techniques will be used, including electron microscopy, morphometry, immunocytochemistry at the electron microscopic level, and autoradiography. These studies will contribute to our understanding of the complex mechanisms involved in normal and abnormal development of the human pituitary gland, particularly with respect to pituitary dwarfism and related growth disorders, as well as to the formation of pituitary adenomas and to various dysplasias involving pituitary target endocrine organs such as the thyroid gland, adrenal glands, and gonads.