In patients with or without various chronic liver diseases, the total urinary excretion of hydroxyproline and hydroxylysine and the hepatic content of hydroxyproline were examined. In 7 patients without liver disease, the urinary excretion of hydroxyproline and hydroxylysine were 10.3 +/- 1.5 and 1.31 +/- 0.21 mmol/mol creatinine, respectively, and the hepatic content of hydroxyproline was 4.9 +/- 0.6 mumol/g of wet liver. In 33 patients with liver disease, the urinary excretion of hydroxyproline and hydroxylysine and the hepatic content of hydroxyproline were increased in proportion to the severity of liver disease. The hepatic content of hydroxyproline showed a significant correlation with the urinary excretion of hydroxyproline and hydroxylysine (r = +0.406 and r = +0.531, respectively). These results suggest that the study of urinary hydroxyproline and hydroxylysine excretion may yield useful information on the metabolism of hepatic collagen in chronic liver disease. Moreover, urinary hydroxylysine excretion seemed to be a better index of hepatic collagen metabolism than urinary hydroxyproline excretion; perhaps urinary hydroxylysine excretion is not much affected by dietary collagen intake.