To date there has been no description of the hemodynamic dose-response relationship betweeO enflurance and sodium nitroprusside (SNP), although these drugs are often used together to induce deliberate hypotension. Utilizing aortic root cannulation and thermistor-tipped pulmonary artery catheters, this relationship was studied in six beagles during 1 and 2% enflurane anesthesia and compared with the hemodynamic response induced by SNP in the awake state and during anesthesia with intravenous morphine (6 μg/kg). Each animal received a standard infusion of 100 μg/kg of SNP administered at three different flow rates (5, 10, and 20 μg/kg/min). SNP infusion resulted in dose-related reductions in mean arterial pressure, systemic vascular resistance and left ventricular stroke work, whereas cardiac output increased. Enflurane potentiated the hypotensive effects of SNP in a dose-related fashion. During morphine anesthesia, however, the hemodynamic effects of SNP were virtually indistinguishable from those observed in the awake state.