In recent years the continuity equation has been established as a valuable non-invasive method for calculating aortic valve area. The continuity equation cannot be used if there is calcification or sub-valvular stenosis in the left ventricle-outflow tract, because the area of the outflow trace is not circular in those cases. The authors have tested the value of a non-invasive variant of the Gorlin formula, as an alternative method of identifying severe aortic stenosis. They examined 32 consecutive patients with aortic stenosis with both methods. Seventeen patients had severe stenosis (valve area < or = 0.7 cm2), calculated by the continuity equation. The other 15 patients had moderate stenosis (valve area 0.7-1.0 cm2). Using the non-invasive variant of the Gorlin formula, the authors were able to identify 16 of the 17 cases with severe stenosis, thus showing that the method is useful for identifying severe aortic stenosis. (P < 0.001 by chi 2-test).