The aim of the study has been to assess if intermittent treatment with norfloxacin could be able to maintain selective intestinal decontamination in cirrhotic patients in order to prevent bacterial infections. Group I (n = 10, subgroup Ia, n = 5, hospitalized cirrhotics, subgroup Ib, n = 5, outpatient cirrhotics) received 400 mg/24 h norfloxacin 7 days. Group II (n = 5, outpatient cirrhotics) received 400 mg/12 h norfloxacin 7 days. Gram-negative aerobic bacilli of the fecal floral were strongly suppressed in all patients at the end of the treatment, and they totally (Group I) or partially (Group II) recovered the initial concentrations 7 days after the end of the treatment. There were not significant differences between subgroups Ia and Ib. These results suggest that prophylactic treatment with norfloxacin in cirrhotic patients at high risk of infection should be continuous during the period in whom patients must be submitted to selective intestinal decontamination.