Effects of enflurane anesthesia were studied on the circulation dynamics and blood catecholamine (CA) concentrations during and after inhalation 2% or 3% enflurane in oxygen in 8 dogs at each concentration. During inhalation, the mean arterial pressure (MAP) and cardiac index (CI) decreased significantly. After stopping inhalation, the MAP recovered rapidly to the control values, but the CI recovered to only 65% of the control values. Immediately after starting inhalation, blood CA concentrations decreased significantly in both groups. After stopping inhalation, blood adrenaline (AD) concentration increased rapidly to 6 and 5 times as the control values in the 2% and 3% groups, respectively. Blood noradrenaline (NA) concentration increased to 3 times as the control values in both groups. One hundred and twenty min after starting inhalation, the dogs did not respond to painful stimulation even in the 2% group. In this study, it has been suggested that the circulation dynamics are suppresed when enflurane has reached more than 0.5 minimum alveolar concentration (MAC) and that the centripetal impulse is thoroughly blocked and CA secretion from the adrenal grand is inhabited at 0.7 MAC of enflurane.