A model of lymphatic conductivity (i.e. flow rate per unit pressure difference = conductance) based on protein-kinetic and haemodynamic measurements is described. The model is applied to data from patients with cirrhosis and from pigs with different haemodynamic abnormalities in the hepatosplanchnic system. In cirrhotic patients without ascites the estimated thoracic duct conductance (gthd) was three times higher than normal whereas this value was close to normal in patients with tense ascites. The estimated conductance of the right lymphatic duct was ten times below that of the thoracic duct in patients with ascites. In pigs gthd was similar to that in normal humans and no change was seen during acute congestion of the liver. In ascitic pigs gthd was low. The estimated conductance of the liver blood-lymph barrier was similar in normal humans and pigs, but decreased in cirrhosis and was thus compatible with increased sinusoidal wall tightening and fibrosis in the interstitial space of the liver. The model presented supports the so-called 'lymph-imbalance' theory of ascites formation according to which a relatively insufficient lymph drainage is important in the pathogenesis of hepatic ascites.