['Pulse dye-densitometry, a novel monitor that measures circulating blood volume (CBV) and cardiac output (CO), was used in patients with pheochromocytoma to determine the relationship between CBV and post resection hypotension.', 'Case control study. An alpha blocker was administered for approximately two weeks, and its effect on the expansion of CBV was quantified. CBV was monitored in seven patients admitted for resection of suspected pheochromocytoma before preoperative alpha-blocker therapy, after alpha-blocker therapy and three times during the operation. Relationships between the CBV and blood pressure after resection of the tumour were examined.', 'CBV increased from 72.0 +/- 10.0 mL.kg(-1) to 83.4 +/- 12.2 mL.kg(-1) after alpha blockade. (P < 0.001). We found a significant inverse relationship between the increase in CBV after alpha-blocker therapy and blood pressure after resection of the tumour.'] Does an increased circulating blood volume prevent hypotension after pheochromocytoma resection?