The types and numbers of bacteria were examined in aspirates from the jejunums of 27 chronic alcoholics and 13 hospitalized control patients of comparable age distribution without alcohol abuse or diseases of the liver. Samples of jejunal juice were aspirated in the fasting state. The mean number of microorganisms obtained during anaerobic incubation was distinctly higher in the alcoholics (log10, mean+/-SD: alcoholics 4.9+/-2.2, controls 3.2+/-1.5, p less than 0.025). A similar difference was found for the number of aerobic bacteria (alcoholics 4.7+/-1.9, controls 3.3+/-2.1, p less than 0.05). Significant counts (greater than 10 (5)/ml) of bacteria obtained during anaerobic incubation were more frequent in the alcoholics (48.1%) than in the controls (7.6%, p less than 0.001). Coliform microorganisms were cultured much more frequently from the jejunal fluid of the alcoholics (alcoholics 55.6%, controls 15.4%, p less than 0.025). In addition the incidence of Gram-negative anaerobic bacteria and endospore-forming rods was higher in the aspirates from alcoholics (p less than 0.05). In both groups the number of microorganisms in jejunal fluid correlated closely with the pH found in the gastric juice. No correlation was found between the numbers or types of microorganisms in the jejunum and the type or degree of liver disease in the alcoholics. It is concluded that bacterial overgrowth might contribute to functional and/or morphological abnormalities of the small intestine commonly found in patients with chronic alcohol abuse.