The effects of Hange-shashin-to (TJ-14) were examined regarding the amount of prostaglandin E₂ (PGE₂) and the water absorbind capacity in the large intestine of rats. Repeated oral administration of TJ-14 at doses of 125 to 1000 mg/kg revealed a significant decrease in PGE₂ content in the colonic mucosa and also the promotion of colonic water absorption in a dose dependent manner. However, there was no remarkable influence on the concentrations of aldosterone and electrolytes in the serum, even at 1000 mg/kg. From these results, it was considered that some of the anti-diarrheal effects of TJ-14 might be based on a repression of the increase in the amount of PGE₂ as well as promotion of the water absorbing capacity of the large intestine. Moreover, it was also suggested that it is possible, by the application of TJ-14, to prevent the loss of water content caused by diarrhea.