Effects of a high subarachnoid block and high epidural block, with and without epinephrine in the anesthetic solution, were studied in the same patients. High subarachnoid block produces hypotension, decreased stroke volume, decreased cardiac output, and a slight decrease in peripheral resistance. High epidural block with epinephrine in the anesthetic solution produces the same degree of hypotension, but an increase in heart rate, stroke volume, and cardiac output and a marked drop in peripheral resistance. High epidural block without epinephrine produces changes similar to, but not as profound as, subarachnoid anesthesia. Unmedicated patients blocked by high subarachnoid anesthesia are able to hyperventilate and maintain normal blood gas tensions.