The cardiovascular effects of Forane, a new inhalation anesthetic, were examined in seven un-medicated volunteers under conditions of constant arterial carbon dioxide tension and body temperature. Comparison of results during anesthesia with awake values demonstrated maintenance of myocardial function but progressive vasodilatation as anesthesia deepened. No significant changes in the cardiac output, ballistocardiogram I-J wave amplitude, ejection time, mean rate of ventricular ejection, or pre-ejection period occurred with onset or deepening of anesthesia. Arterial pressure decreased, as did total peripheral resistance. Increased muscle and skin blood flow and forearm venous compliance suggested that the loss of resistance was due in part to dilatation of vessels in the skin and muscles. Cardiac output was maintained by an increased heart rate which compensated for the decreased stroke volume. Comparisons of results during the first and fifth hours of anesthesia demonstrated only minor changes with increased duration of anesthesia. These included further increases in forearm blood flow and an increase in base excess.