The response of the adrenal medulla in anesthetized dogs to hemorrhagic hypotension of a varied level and duration was observed to be primarily accompanied by a highly significant increase in adrenal plasma epinephrine. On the other hand, the secretion of norepinephrine had an unpredictable occurrence in adrenal blood samples collected in periods of hypotension. The essential determinant of adrenal blood flow was observed to be the level of mean blood pressure. While this relationship was not in strict proportion, changes in mean blood pressure were invariably followed by changes in adrenal blood flow in the same direction. The adrenal medulla of dogs in hemorrhagic irreversible shock was observed to continue to secrete epinephrine at very low levels of mean blood pressure, characteristic of terminal shock. Reports by other groups of investigators on elevated peripheral blood levels of epinephrine in hemorrhagic shock have been found to result mainly from an actively secreting adrenal medulla.