Helicobacter pylori gastric infection has been associated with various digestive and extradigestive diseases. In liver disease bacterial infections have been associated with impairment of cytochrome P-450 liver metabolic activity. Moreover, infection by Helicobacter spp. seems to be linked with the development of hepatocellular carcinoma (HCC) in mice. Our aims were to evaluate the influence of H. pylori infection on cytochrome P-450 liver metabolic activity as assessed by means of monoethylglycinexylidide (MEGX) test and to assess the prevalence of H. pylori infection in patients with HCC. Ninety-six hepatitis C virus (HCV) -positive cirrhotic patients, 36 of whom had HCC, were tested for H. pylori infection by means of anti-H. pylori IgG. Patients underwent the MEGX test. Characteristics of the patients were then analyzed on the basis of the presence of H. pylori infection. Seroprevalence of H. pylori infection was similar between cirrhotic patients without (68%) or with (63.8%) HCC. Mean MEGX values were significantly (P < 0.0001) lower in H. pylori infected patients (18.2 +/- 13.9 ng/ml) as compared to the noninfected ones (46.9 +/- 17.1 ng/ml), independently of Child-Pugh's classification. These differences persisted even after subdividing patients according to the presence of HCC. In conclusion, in anti-HCV positive cirrhotic patients H. pylori infection is associated to an impairment of cytochrome P-450 liver metabolic activity. Seroprevalence of H. pylori infection in HCC patients is similar to that observed in tumor-free cirrhotics.