Neurohumoral effects of head-up tilt (HUT) induced hemodynamic responses, with or without pharmacological blockades, are well known. However, little is known about the modulation of theses cardiovascular responses during catecholamine hormone infusions. We investigated how continuous epinephrine infusion modulates HUT induced cardiovascular responses using two passive 5 min 70° HUT trials: A control run (without infusion) and a supplemented run (with prior epinephrine infusion, titrated to a dose which increased supine mean arterial pressure by 20% above resting values). This randomized study was carried out in eight healthy male volunteers and each trial was separated by two weeks. Compared to the control run, epinephrine infusion increased basal heart rate by 17 bpm, systolic pressure by 19 mm Hg and stroke volume index by 12.6 ml/m², whereas diastolic pressure and thoracic impedance stayed unchanged. Despite similar HUT induced thoracic fluid shifts, reflected by the thoracic impedance changes, the epinephrine infused group showed no significant changes in heart rate and stroke volume index compared to the controls. An increase in total peripheral resistance during HUT in epinephrine treated subjects elevated the diastolic blood pressure, an effect not observed in the controls. This suggests that during epinephrine infusion supine blood pressure is maintained primarily by changes in cardiac functions, whereas during HUT vascular resistance appear to play a more important role.