The effects of stress on plasma corticosterone and growth hormone (GH) were determined in adult female rats 24 h after forebrain removal in order to study the anatomical substrate essential for stress-induced alteration of pituitary function. Rats with median eminence-pituitary islands (MEPI) showed significant increments in plasma corticosterone levels 15 min after immobilization-blood withdrawal stress. Rats with basal hypothalamic-pituitary islands (BHPI) showed comparable increments, suggesting that the presence of hypothalamic tissue in addition to median eminence did not enhance the steroid response. A subsequent study demonstrated that MEPI rats are capable of a 2nd response, 6 h after thefirst. MEPI rats also showed a significant 50% increase in plasma GH levels 15 min after immobilization-blood withdrawal. In a final experiment, MEPI rats showed corticosterone but not GH responses to immobilization applied without blood withdrawal. These data offer further evidence that some stressful stimuli can alter pituitary functions under short-term conditions in the absence of hypothalamic or other forebrain neurons.