A novel quantitative liver function test is described which is based on monoethylglycinexylidide (MEGX) formation after lidocaine bolus injection. Following the administration of small single doses of lidocaine hydrochloride (1 mg/kg), monoethylglycinexylidide serum concentration-time curves were determined by a novel highly sensitive fluorescence polarisation immunoassay (FPIA) in healthy volunteers, liver donors and patients with liver cirrhosis. The FPIA allowed rapid and reliable monoethylglycinexylidide determinations in serum and urine (between-days coefficient of variation: less than 10.3%, recovery: 80-113%). Monoethylglycinexylidide concentrations measured by FPIA in 32 serum samples from patients correlated well those determined by HPLC. The monoethylglycinexylidide concentration in serum determined 15 min after a lidocaine bolus injection proved to be a highly sensitive and specific indicator of hepatic dysfunction. Average monoethylglycinexylidide concentrations in serum obtained 15 min after lidocaine injection were substantially lower in patients with liver cirrhosis than in healthy volunteers. The average monoethylglycinexylidide concentrations in serum were also substantially lower in liver donors with ballooning or fatty changes of hepatocytes than in donors without relevant alterations of liver histology. By means of monoethylglycinexylidide formation in the liver donors, primary function of the transplanted liver was correctly predicted in 32/37 cases and initial non-function in 4/6 cases.