SummaryBilateral electrolytic lesions of hippocampus, amygdala or habenula of the rat did not produce notable changes in pituitary gonadotropic or thyrotropic activity as judged by testicular or thyroid weight and histology and I131 uptake. In response to immobolization stress, PFC levels of normal rats increased 200% after 30 min; after placement of lesions in amygdala, the response to stress was markedly delayed, but eventually reached a 200% increase after 4 hrs. Lesions of hippocampus did not alter the temporal pattern of response to stress; resting or basal PFC levels were, however, significantly higher than normal.