In patients with coronary-artery disease, low concentrations of halothane (arterial concentration 4 to 4.4 mg./100 ml.) added to morphine (1 mg./kg.) anesthesia produced progressive decreases in mean arterial pressure (15.6 percent), heart rate (21.5 percent), stroke volume index (18.4 percent), and cardiac index (35.5 percent), over control values. The maximum decreases occurred after 15 to 30 minutes of halothane administration. These circulatory changes were not prevented by intravenous atropine (0.6 mg.) 3 minutes before administering halothane. The magnitude of circulatory changes was similar to that previously described for healthy volunteers anesthetized with much higher concentrations of halothane (1 percent alveolar or equivalent to about 18.8 mg./100 ml. in the arterial blood).