Diffuse hepatic cirrhosis develops in rats on a choline-deficient diet within 300 days. Absorbable broad spectrum antibiotics added to the daily diet do not prevent the development of fatty infiltration, but they delay the development of cirrhosis for about 100 days more. Non-absorbable antibiotics added to the daily diet prevent the development of cirrhosis in most rats for as long as 750 days. The superiority of non-absorbable antibiotics to absorbable antibiotics excludes a systemic effect of the antibiotics and demonstrates that intestinal bacteria are largely, if not wholly, responsible for the cirrhosis in rats on a choline-deficient diet.