A new method of assessing the severity of aortic regurgitation severity by magnetic resonance imaging has been developed. Two groups were studied: 20 controls (age = 58 +/- 19 years) without valvular aortic disease, and 24 patients (age = 62 +/- 13 years) with chronic aortic insufficiency evaluated by magnetic resonance and aortic root cineangiography within 1 week of each other. A magnetic resonance sequence (TR = 35 ms/TE = 12 ms/flip angle = 20 degrees/magnet = 1.5 T) was acquired in a plane containing the thoracic aorta. A transverse saturation band 30 mm wide was positioned 30-40 mm above the aortic valve. Aortic insufficiency was graded; the importance of end-diastolic retrograde movement in the saturation band in the descending aorta was noted. Magnetic resonance was also compared to Doppler echocardiography in 20 patients. In the controls, we found that retrograde blood flow was absent (18/20) or mild (2/20). In contrast, the presence of marked retrograde movement in a saturation band across the thoracic aorta was always associated with severe aortic regurgitation (angiographic grade III or IV). This rapid method (imaging time less than 20 min) can be applied in most patients with aortic regurgitation and is likely to be helpful when echocardiography is not possible or gives inconclusive results.