Circulatory responses following intravenous diazepam (0.5 mg/kg) and the subsequent addition of 50% nitrous oxide were studied in 14 patients undergoing elective aortocoronary saphenous vein bypass operations. No patient was receiving propranolol. Preanesthetic medication was with morphine and scopolamine. Diazepam was continuously infused over a 10-minute period. At the conclusion of the infusion, systolic and mean arterial pressures were 13% lower than control awake values (p less than 0.05). Heart rate, cardiac output, right atrial pressure, pulmonary arterial pressure, pulmonary artery occluded pressure, and systemic and pulmonary vascular resistance were not changed. The subsequent addition of nitrous oxide resulted in no further statistically significant changes except for a 2.4 torr increase in right atrial pressure (p less than 0.05). In contrast, previous data collected from similar patients demonstrated significant reductions in blood pressure and cardiac output while systemic and pulmonary vascular resistance and pulmonary artery occluded pressure were increased when nitrous oxide was added following the administration of morphine (1 to 2 mg/kg). It is concluded that the observed minimal circulatory changes following diazepam administration and the subsequent addition of nitrous oxide make diazepam-nitrous oxide a valuable alternative to a morphine-nitrous oxide induction of anesthesia in patients with coronary artery disease.