The site of action and the pathways of adrenaline after stress have been studied by using H3 labeled adrenaline. In this study the stress was induced in rats by producing fractures of the long bones and also by administering exogenous adrenaline in different doses. Animals were sacrificed at the interval of 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 12 hours and 24 hours after producing stress. All animals were injected with 25 microcuries of radioactive adrenaline intraperitoneally before the production of stress. After sacrificing the animals, the brain, all the endocrine glands, the heart, the liver and the kidney were subjected to microautoradiography. We could localize the particular cells in the hypothalamus (PVN) which could be responsible for the endocrine and metabolic changes in the body after stress. The radioactive adrenaline granules could be seen in the various tissues at different intervals, including the thyroid gland, adrenal gland, heart muscle, liver, kidney, etc., suggesting the site of action of adrenaline on these tissues at different periods.