The aim of this study was to evaluate the efficiency of pulmonary gas exchange during the course of liver transplantation. We studied 25 adult cirrhotic patients undergoing transplantation, performed with venovenous bypass. A significant increase in PaO2, and a significant decrease in physiological shunt and alveolar-arterial partial pressure difference were observed just before the start of venovenous bypass. These changes were probably caused by modifications in respiratory mechanics, such as an increase in functional residual capacity. There were no other respiratory changes during the anhepatic and post-anhepatic phases.