• The central plasma clearance rate of amino acids (CPCR-AA), the ratio of peripheral amino acid entry rate into blood plasma to arterial amino acid concentration, was measured preoperatively in 149 noninfected cirrhotic patients. In 50 survivors of shunting or general surgical procedures, the mean (±SEM) CPCR-AA was 201±17 mL/m2 min; in 39 subsequent deaths, the mean ratio was 87±14 mL/m2 min. Comparing Child's classification with CPCR-AA reveals the following values: class A (mortality, two of ten patients) survivors, 152±23 mL/m2/min; class A deaths, 96±54 mL m2 min; class C (mortality, 13 of 19 patients) survivors, 214±47 mL/m2/min; class C deaths, 101 ±13 mL m2 min. The preoperative CPCR-AA of 46 patients receiving liver transplants was 91 ± 9 mL/m2/min; 69% of these patients survived. Preoperative CPCR-AA values correlated significantly with rates of hepatic protein synthesis in incubated liver slices obtained by biopsy at operation in 22 patients. Thus, CPCR-AA determination is a true liver function test, valuable in predicting surgical mortality and selecting transplantation or other operations for cirrhotic patients. (Arch Surg 1987;122:468-473)