Because the posterior pituitary gland is joinedto the anterior pituitary by the short portal vessels and con-tains both corticotropin and corticotropin-releasing factors, it could play a role in regulating adrenal hormone release. To clarify this, we studied the function of the brain-adrenal system, with and without the posterior pituitary, by determining glandular weights and plasma corticosterone concentrations. Studies were done under different conditions of anterior pituitary stimulation: (1) in the basal state; (2) after altered negative feedback (unilateral adrenalectomy); and (3) under different types and intensities of stress. All the studies were carried out in unanesthetized rats several weeks after either posterior hypophysectomy [i.e., neuro-intermediate lobectomy (NI-hypox)] or a sham operation. The findings demonstrate that the hypothalamic-anterior-pituitary-adrenal system functions normally in the absence of the posterior pituitary gland. Larger sex organs were found in unilaterally adrenalectomized, M-hypox male rats than were found in the sham-operated controls.