The pituitary gland controls directly or indirectly the activity of almost all endocrine glands, and by its connections with the hypothalamus it is associated with sensorial-visceral and autonomic processes. These characteristics make this gland a major integrator of homeostatic mechanisms. The immune response may be considered as a homeostatic response since antigens elicit an immune response not only because of their potential risk for the host (harmless foreign agents can be good immunogens), but also because it leads to a perturbation of the “milieu interieur”. The capacity of the immune system to discriminate between self and non-self has its basis in the wide range of specificities expressed by immune cells, a high proportion of which is directed towards recognition of modified or altered self-cells or -molecules. This characteristic of the immune system implies that it can perceive an internal image of body constituents and react to particular distortions of this image. The immune response as a homeostatic response is therefore under physiological conditions contributing to the maintenance of the constancy and integrity of body cells and tissues. This concept also suggests the participation of neuroendocrine mechanisms in immunoregulation and thus, integration at the pituitary level as well.