During mammalian anterior pituitary development, the pituitary-specific transcription factor Pit-1 has an important role in the regulation of the initial expression of GH, PRL, and TSHbeta encoding genes and in the development of the lactotropes, somatotropes and thyrotropes which produce PRL, GH, and TSH respectively. It is also known that Pit-1 is involved in the hypothalamic regulation of these pituitary hormones, both at pre- and postnatal stages. However, little is known about the structure, the initial expression and the regulatory functions of Pit-1 in avian species. In this work, the structure and the initial appearance of the chicken Pit-1 gene, and its involvement in the hypothalamic regulation of pituitary hormones are described. A newly developed quantitative assay is described which allows the study of the regulatory role of Pit-1 within the hypothalamus-pituitary axis in chicken. The results and hypotheses presented in this book should be useful to unravel even more of the complex interactions between the hypothalamus, the pituitary and several endocrine organs.