A population of cells in the pars anterior that stain with acidic dyes synthesize and secrete somatotropin for delivery to its receptors located in several tissues of the body. The first known action of somatotropin was to increase growth in body size of normal as well as hypophysectomized rats. This chapter discusses the endocrinology of growth hormone (GH) secretion as well as the neurohormonal regulation and neuroendocrine integration of adenohypophysial release of GH. The adenohypophysial cells that synthesize and secrete GH are known as somatotrophs. Specific binding of radiolabeled GH to homogenates of various tissues suggested a large number of target tissues. The term insulin-like growth factor was assigned to the identified somatomedin polypeptides because of structural homology with the beta chain of the insulin molecule. Stressful stimuli affect release of adenohypophysial GH in ways that vary widely among species.