A nuclear magnetic resonance (NMR) flowmeter has been developed for noninvasive measurement of upper extremity blood flow in humans. Flow through major arteries and veins is determined by placing the arm into a 12.5‐cm i.d. crossed‐coil detector structure, contained in a 0.075 T (750 G) steady detector field. Venous flow is measured by passage of a demagnetized bolus of blood, generated by periodic application of a radio‐frequency tagger field upstream from the detector. The self tag technique is applied to arterial flow. Detector output is a direct function of the pulsatile component of arterial volume flow, within the range of linear operation. Consideration has been given in flowmeter design to sensitivity, long term stability, and ease of operation.