Aims: To evaluate the usefulness of plasma hydroxy-metronidazole/metronidazole (OH-MET/MET) ratios as a dynamic liver function test in ethanol abusers with or without liver cirrhosis. Methods: Metronidazole was administered intravenously for 20 min to healthy volunteers, and to patients with alcohol-induced, non-cirrhotic hepatopathy and liver cirrhosis. Plasma concentrations of metronidazole and hydroxy-metronidazole were measured by high performance liquid chromatography in samples collected 5, 10, 20 and 30 min after the metronidazole infusion. Results: Patients with non-cirrhotic alcoholic hepatopathy had significantly elevated aminotransferase levers compared to healthy volunteers and Child A patients. Child-Pugh C patients had significantly prolonged prothrombin times when compared to healthy volunteers and patients with non-cirrhotic hepatopathy. Metronidazole metabolism, as measured by the OH-MET/MET ratio following the intravenous administration of 500 mg of the drug, was significantly impaired in all ethanol-abusing individuals, including patients with non-cirrhotic alcoholic hepatopathy. Conclusions: Metronidazole metabolism was impaired in ethanol abusers, even in the absence of liver cirrhosis, indicating that ethanol was capable of affecting liver function in the early stages of alcohol-induced liver disease.131013351341