A block in the transsulfuration pathway has previously been suggested in cirrhosis on the basis of increased fasting methionine concentrations, decreased methionine elimination and low levels of methionine end products. To date, methionine elimination has never been studied under controlled steady-state conditions, and the relation of the severity of liver disease to impaired methionine metabolism has not been clarified. We measured methionine plasma clearance in 6 control subjects and in 12 patients with cirrhosis during steady-state conditions obtained by a primed, continuous methionine infusion. In the presence of high-normal fasting methionine concentrations (range = 14 to 69 μmol ± L−1 in controls and 26 to 151 μmol ± L−1 in cirrhotic patients), methionine plasma clearance was reduced in cirrhotic patients (2.25 ± S.D. 0.43 ml ± sec−1 vs. 2.86 ± S.D. 0.43 ml ± sec−1 in controls; p < 0.05), whereas methionine half-life was increased (282 ± 90 min vs. 187 ± 25 min in controls; p <0.05). Fasting methionine significantly correlated with methionine clearance. The infused methionine was not degraded to urea to any significant extent in cirrhotic patients, whereas a threefold increase in urinary urea nitrogen excretion rate was observed in controls. Similarly, taurine concentrations significantly increased both in plasma and in the urine in controls but not in cirrhotic patients. In cirrhotic patients methionine plasma clearance significantly correlated with galactose elimination capacity (r = 0.818) and with the Child-Pugh score (rs = −0.795). The study supports a major role of impaired liver cell function in the reduced metabolism of methionine and decreased formation of methionine end products that occur in cirrhosis. Impaired methionine metabolism is probably the basis for the hypermethioninemia of advanced cirrhosis. (HEPATOLOGY 1992;16:149–155.)