The aim of this study was to define that the expression of inducible nitric oxide synthase (iNOS)in cell blocks from ascites was a certain value to evaluate hepatopulmonary syndrome(HPS). iNOS can stimulate the liver and lung to produce excess NO. Excessive production of NO can cause pulmonary vasodilatation and impaire arterial oxygenation. HPS is characterized by shortness of breath and hypoxemia caused by impaired arterial oxygenation due to pulmonary microvascular dilatation in patients with liver disease or PTH. Therefore.the positive rates of iNOS was a certain value to evaluate the conditions of HPS.