1. The influence of weak mechanical stimulation of the jejunal mucosa in vivo on PGE-release, on intestinal blood flow and transmucosal water movement was studied in rats. 2. Mechanical stimulation of the mucosa increased PGE-release into the venous outflow and into the gut lumen. This increase is followed by an increase in intestinal blood flow and transmucosal movement of tritiated water in both directions. 3. Pretreatment of the rat with indomethacin reduced the effect of mechanical stimulation on PGE-release. Indomethacin further reduced the increase in blood flow and in secretion of tritiated water. Absorption of tritiated water was not changed in these experiments. 4. Pretreatment of the rat with atropine (1 mg/kg, i.p.) or perfusion of the gut with methysergide (10 microgram/ml) did not influence the increase in intestinal blood flow after mechanical stimulation. 5. It is suggested that enhanced intestinal blood flow and transmucosal movement of tritiated water after mechanical stimulation are mainly provoked by a preceding release of PGE. 6. It is further supposed that such a mechanism may be physiologically involved in regulation of intestinal blood flow and transmucosal water movement during food intake.