The influence of bacteria on metabolism of collagen in the colonic wall under normal conditions and after obstruction was evaluated by using germ-free and conventionally bred rats. Under normal conditions, no differences in synthesis and content of collagen or tissue dry weight in the colonic wall were found between germ-free and conventionally bred rats. After obstruction, both groups reacted similarly with an equally increased collagen synthesis. The findings imply that bacteria do not play any major role in the regulation of collagen metabolism in the colonic wall, neither under normal conditions nor in the strained situation with colonic obstruction and fecal impaction.