30 patients (24 fm, 6 m) with angiographically proven mitral stenosis as well as 10 healthy controls were investigated by wedge catheterism and thallium-201-scintigraphy to calculate the heart-lung quotient of the isotope. All patients with mitral stenosis could be discriminated from controls by a pathological increase of isotope concentration in the lungs. 4 groups could be subdivided: the first consisted of 8 patients with normal pulmonary artery pressure of x = 13.06 mm Hg and a normal heart-lung quotient less than 1.1. The second group of 15 patients showed passive pulmonary hypertension with a PAm of x = 27.57 mm Hg and heart-lung quotients between 1.1 and 1.4. A third group of 9 patients showed PAm of 36.76 mm Hg with reactive hypertension and a HLQ between 1.4 and 1.6. The last group of patients showed pulmonary hypertension of x = 45 mmHgPAm and a heart-lung quotient of greater than 1.6. Scintigraphy alone allowed classification of the patients, so the value of this method is proven for pre- and postoperative strategy.