Total blood volume (TBV), red cell volume (RCV) and plasma volume (PV) were determined in 15 pheochromocytoma patients (9 males and 6 females) prior to and during preoperative treatment with phenoxybenzamine. Seventeen healthy male volunteers served as controls. Untreated male patients did not differ from the controls with respect to TBV, RCV or PV. In the total group of pheochromocytoma patients, phenoxybenzamine, in a dose of 145.6 +/- 45.2 (SD) mg/day over 14.3 +/- 5.7 (SD) days, induced significant increases in TBV (+9.4%) and PV (+14.5%), whereas RCV remained unchanged. During phenoxybenzamine, the mean PV in male patients significantly exceeded the control mean. We conclude that pheochromocytoma patients adapt their TBV to excessive catecholamine production and that they rarely present with profound hypovolemia. Moderate but higher doses of phenoxybenzamine than previously recommended induced marked increases in TBV secondary to PV expansion. Phenoxybenzamine counteracts the development of hypovolemia most effectively, thereby constituting one of several important measures for successful surgical management of pheochromocytoma patients.