A technique for measuring blood flow by whole body nuclear magnetic resonance is described. This method uses imaging gradient profiles that combine even echo rephasing with a field echo sequence to overcome the problem of signal loss from flowing blood. The flow velocity component in any desired direction may be measured by appropriate gradient profile modifications, producing velocity dependent phase shifts that can be displayed by phase mapping. The sequence allows for fast repetition so that flow information may be acquired rapidly from many points in the cardiac cycle and has been used in this mode to observe and measure blood flow in the heart chambers and great vessels. Flow measurements in the femoral artery were also carried out using the same technique; these were compared with similar measurements obtained by Doppler ultrasound. The technique can readily be applied using standard imaging equipment and should prove useful in the clinical assessment of many diseases of the cardiovascular system.