We measured serum erythropoietin (EPO) immunoenzymatically in 245 subjects (151 male, 94 female) to investigate the pathophysiology of its liberation in patients with liver disease. Twelve patients had acute hepatitis, 60 mild chronic liver disease (CLD), 50 cirrhosis (CIR), 43 hepatocellular carcinoma (HCC), 16 malignant extrahepatic disease, 32 benign extrahepatic disease (BEN); 32 subjects served as healthy controls. Higher EPO levels were found in all groups of patients as compared with controls (Bonferroni's test, P < 0.01); CIR and HCC had higher values than CLD and BEN (P < 0.01). By multiple regression analysis, EPO correlated with haematocrit, cholinesterase and C-reactive protein (F = 18.63, P < 0.0001). Thus, circulating EPO increases in patients with liver disease, particularly in its more advanced forms. Besides anaemia, both impairment of liver function (possibly via decreased EPO metabolism) and inflammation seem to play contributory roles in elevating serum EPO.