Background: Small intestinal bacterial overgrowth generates endogenous ethanol production both in experimental animals and humans. Patients with cirrhosis have small intestinal bacterial overgrowth, but endogenous ethanol production has not been studied in them. Aim: To investigate endogenou ethanol production in patients with cirrhosis, altered intestinal motility and small intestinal bacterial overgrowth. Patients and methods: Eight patients with cirrhosis of different etiologies and altered gastrointestinal motility, consisting in changes in the migrating motor complex, were studied. All had also small intestinal bacterial overgrowth, measured by means of the H2 breath test with lactulose. Plasma ethanol levels were measured by gas liquid chromatography in fasting conditions and 120 min after a carbohydrate rich meal. Results: In fasting conditions, no patient had endogenous ethanol production. Alter the meal, ethanol in concentrations of 11.3 and 8.2 mg/del were detected in two patients. Negligible amounts of ethanol were detected in 4 patients and two patients had undetectable alcohol levels. Conclusions: A low endogenous production of ethanol was demonstrated in six of eight patients with cirrhosis (Rev Méd Chile 2002; 130: 1329-34)