We purposed to evaluate the effects of A1 blockade (Urapidil) on the renal blood flow and consequent renal function by using the 2-D-color Doppler technique. The subjects were 13 healthy male volunteers (average: 35 years old; 25-44) and 15 hypertensive cases (6 males and 9 females, average: 59 years old; 45-75). 30 mg and 45 mg A1 blockade (Urapidil) had been randomly given to these controls and patients. Blood pressure, heart rate, and renal blood flow were measured after a 30-minute rest, before the administration of the drug, and one and two hours after the administration. To measure the renal blood flow, ultrasonic diagnostic equipment SSA-270A (Toshiba Co., Ltd.) with a sector electric-phased 3.75 MHz. array probe was used. Doppler siftgrams of the interlobar artery (ILA) in the right kidney were recorded. Then, we calculated their velocities and parameters. (1) controls: In the 30 mg group, both renal blood maximum velocity (Vmax) and minimum velocity (Vmin) of ILA did not show significant changes although the Vmax/Vmin ratio and resistance index tended to decrease. In the 45 mg group, although both Vmax and Vmin were subject to significant reductions, the Vmax/Vmin ratio and resistance index showed no significant changes. (2) patients: In hypertensive groups (both 30 mg and 45 mg), neither Vmax nor Vmin of ILA showed any significant changes although the Vmax/Vmin ratio and resistance index showed significant reductions. In particular, the resistance index was proportional to vascular resistance. This reduction meant a reduction of vascular resistance of the ILA, namely the expansion of the vascular diameter, indicating that it may lead to an increase of renal blood flow in the case of constant velocity. Our results indicated that in hypertensive cases, the administration of A1 blockade (Urapidil) led to a significant increase of renal blood flow, suggesting that A1 blockade may affect renal function favorably.