Publisher Summary This chapter discusses several aspects of morphofunctional relationships of the developing human pituitary glands with special emphasis on the findings of immunohistochemical techniques. Nakane's peroxidase-labeled antibody method is the immunohistochemical technique used at light and electron microscopic levels. The rapid progress in complementary DNA recombinant technique that demonstrates the larger precursor molecule for adrenocorticotropic hormone (ACTH) is described in the chapter. Biochemical studies on hypothalamic tropic hormones have progressed dramatically. Luteining hormone and somatostatin are among the classic hormones with known amino acid sequences. Corticotropin releasing factor and growth hormone releasing factor are recently identified hypophysiotrophic peptides. It has been shown that nonhypophyseal organs also produce the same peptides as those synthesized in the pituitary gland. ACTH and its precursor are good examples and have been shown to be produced in the hypothalamus. Some human tumors, such as lung cancers, have also been shown to secrete ACTH and its precursor.