The adrenal medullary catecholamine response to graded hemorrhage has not been characterized in awake animals. Using high performance liquid chromatography with electrochemical detection, secretion rates of epinephrine and norepinephrine were measured in trained awake dogs with chronic adrenal venous cannulas. The results indicate that the adrenal medulla responds to small and moderate hemorrhages, and the magnitude of the response is directly related to the magnitude of the hemorrhage. The epinephrine secretory response is greater than the norepinephrine secretory response. The response pattern is biphasic, with an early response by 10 min and a late response by 30 min after the onset of hemorrhage. Finally, the adrenal medullary system appears to have the potential to produce a memory of earlier stimuli, since the response to a small hemorrhage is potentiated if the hemorrhage is preceded by 24 h by a moderate hemorrhage.