A newly developed pulsed ultrasound Doppler meter was used for measurement of blood flow in aortocoronary vein grafts during operation. The results were compared with measurements obtained with conventional electromagnetic flowmetry. In 27 grafts, excellent agreement was found between electromagnetic flow probes thoroughly calibrated for varying hematocrit on fresh veins in vitro, and a clip-on type of Doppler probe (r = 0.86). In vitro calibration showed a close correspondence (r = 0.98) with the Doppler technique with no dependency on hematocrit and no need for zero calibration. The use of a conventional electromagnetic flowmeter showed strong dependency on recent calibration, both for saline and for varying hematocrit. Zero-calibration was necessary for every single graft measurement. The application of ultrasound Doppler meters of high quality together with clip-on probes of proper design proved to be superior to electromagnetic flowmetry for intraoperative blood flow measurements.