The cardiovascular effects of 3 and G per cent alveolar concentrations of diethyl ether in nine healthy young volunteers during the first and fifth hours of anesthesia were studied. Pac*was maintained at 35–39 torr and esophagcal temperature at 36 ± 0.5 C. Cardiac output was unchanged or increased at 3 and 6 per cent ether during the first hour; heart rate increased while stroke volume fell. During the fifth hour of anesthesia, cardiac output increased at both 3 and 6 per cent ether, heart rate increased further, and stroke volume rose to the awake value. Total peripheral resistance was initially unchanged but fell with duration of anesthesia. The ratio of cardiac output to oxygen consumption was unchanged at one hour and increased at five hours. Base excess fell slightly initially and slightly more by five hours.