Continuous direct arterial blood pressure (intra-brachial) recording (CDPR) was performed in the ward in 7 patients with documented pheochromocytoma (PHEO). They consisted of 4 patients with adrenal medulla and 3 with ectopic PHEO in the urinary bladder. Recordings were also taken from 11 patients with mild and moderate essential hypertension (EHT). The arterial pressure variations throughout the day and night were detected for either 24 hours or 48 hours unrestrictive recording (CDPR) transmitted by telemetry (SANEI INST. 270), and analyzed by signal processor (SANEI 7T17). The measurement through CDPR was repeated in all the patients with PHEO on three occasions; (1) observation period (non-medication period), (2) medical treatment period with prazosin and, (3) post-operative period. RESULTS (1) In the non-medication period, all the patients with PHEO were characterized by a steep elevation of the arterial pressure and a variability of the high blood pressure events more remarkably than the patients with EHT. The changes in arterial pressure in the patients with PHEO were accompanied by headaches, feelings of fear, trembling, sweating and palpitation. (2) At the medication period, prazosin sufficiently suppressed the sudden elevation of blood pressure. However, the paroxysmal elevation of blood pressure after voiding was not prevented in 2 of 3 patients with ectopic PHEO in the urinary bladder. Urinary and plasma catecholamine (CA) were normal in 2 of our 3 cases. Voiding elevated plasma CA which provided better diagnostic determinant in patients with this bladder tumor as well as the CDPR. (3) The CDPR provided good operative removal results through the 24-hour monitoring, and the recovery was uneventful. CONCLUSIONS Evaluation of blood pressure elevation is a clue to the diagnosis of hypertension. Monitoring of the arterial blood pressure variation through 24 hours by CDPR was helpful for detecting a precise arterial pressure fluctuation, since the duration of the elevation was short and was steeply changed especially in patients with PHEO.