Abnormalities of pulmonary gas exchange are common in patients with advanced liver disease. Since arterial blood hypoxemia is an important issue in the preoperative evaluation of liver transplant candidates, the study was undertaken to determine the incidence and severity of lung function impairment with a special emphasis on pulmonary gas exchange abnormalities in this group of patients. 104 consecutive patients (47 F and 57 M, mean age 46 +/-11 yr) listed for orthotopic liver transplantation participated in this prospective study. All patients underwent evaluation including: clinical assessment (Child-Pough and MELD classification), chest X-ray, chest sonography, lung function tests, arterial blood gases measurement, and transthoracic contrast enhanced echocardiography. There were 2 patients with acute hepatic failure, 6 patients with primary or metastatic liver carcinoma, and 96 patients with chronic liver disease. The mean PaO(2) and lung function parameters for the entire group were within normal limits. There were 29 hypoxemic patients (PaO(2)< 80 mmHg) and 40 patients with widened (>20 mmHg) P(A-a)O(2). DL(CO) was significantly lower in cirrhotic vs. non-cirrhotic patients (76.5 +/-19.3 vs. 92.4 +/-19.0% predicted; P<0.001). Hepatopulmonary syndrome (HPS) was recognized in 23 (24%) patients. 91% of patients with HPS showed mild to moderate stage of disease. There were significant difference between differences HPS patients and non-HPS patients in DL(CO) (69.0 +/-14.5 vs. 83.5 +/-20.7, P<0.01). In conclusion, all patients referred for OLT should be screened for gas exchange abnormalities. Such a workup should include not only PAO(2) but also DL(CO) and P(A-a)O(2) measurement together with contrast enhanced echocardiography.