Radial arterial spasm in uremic patients undergoing construction of internal arteriovenous (AV) dialysis fistulas was investigated transcutaneously using ultrasonic Doppler flowmetry. In 5 of 15 patients, radial arterial blood flow was significantly decreased 5 min after anastomosing the radial cephalic vein with the radial artery (14.3 +/- 4.5%, mean +/- SE, of the initial value; p < 0.001 vs. the initial blood flow), indicating vasospasm. Vasospasm disappeared 20 min after anastomosing. In 10 patients who were continuously given nicardipine intravenously (1 microgram/kg/min) during surgery, vasospasm did not occur. Arterial blood flow was significantly increased in patients who received nicardipine as compared with patients who did not receive nicardipine and did not have vasospasm, both at 10 min (171.2 +/- 16.2 vs. 124.3 +/- 11.9%, p < 0.05) and at 20 min (176.5 +/- 17.6 vs. 130.2 +/- 11.2%, p < 0.05) after anastomosing. Mean blood pressure was significantly reduced without causing hypotensive symptoms in patients who received nicardipine as compared with patients who did not receive nicardipine and did not have vasospasm. Our study suggests that ultrasonic Doppler flowmetry is useful for diagnosing vasospasm in patients undergoing the creation of AV fistulas and that nicardipine may be effective in preventing vasospasm safely.