Surgical treatment of pheochromocytoma is associated with a high risk of hemodynamic instability. To reduce the risk of perioperative complications, adequate medical treatment to normalize blood pressure and restore blood volume is required. Accurate evaluation of the circulating blood volume (CBV) in perioperative patients with pheochromocytoma is clinically important. In the present study, we adopted whole-body bioimpedance monitoring technique using the Non-Invasive Cardiac System (NICaS), which can non-invasively measure cardiac output (CO) values. NICaS-derived CO values were evaluated in eight preoperative patients with pheochromocytoma and were compared with simultaneous CBV values measured by a conventional indicator dilution method using I-131-labeled human serum albumin. In these patients with pheochromocytoma, the NICaS-derived CO values were significantly correlated with the CBV values measured by I-131-labeled human serum albumin (4.86 +/- 1.05 L/min vs 4.79 +/- 1.02 L; r = 0.906; P = 0.002). Sequential NICaS-derived CO values confirmed that CBV increased after preoperative treatment with an alpha-blocker, with or without volume loading. The results of this study indicate that NICaS can be used to accurately and non-invasively evaluate the hemodynamic status. By sequential monitoring of NICaS-derived CO values, we are able to confirm whether adequate CBV in a patient with pheochromocytoma is obtained by preoperative medical treatment with alpha-blockers or volume loading, to avoid perioperative complications.