Benzodiazepine-like compounds are present in trace amounts in the blood of normal subjects and increase in liver cirrhotic patients with or without encephalopathy. Their increased presence may, however, represent an occasional precipitating factor of hepatic encephalopathy. The source of these compounds is still unknown, but they are constituents of our diet since benzodiazepine receptor ligands have been described in plants, vegetables and in animals. They may also be synthesized, at least in part, by intestinal bacterial flora. In this article we report that the level of these compounds in the blood decreased by 40% after therapy with rifaximin, which reduces the aerobic and anaerobic intestinal bacterial flora. This observation indicates that intestinal bacterial flora is involved in the production of these compounds and that repeated short-term medications with this non-absorbable antibiotic may be useful in reducing the levels of benzodiazepine-like compounds in patients with liver cirrhosis.