The stress ulcer formation is enhanced significantly in rats operated with pyloro-jejunostomy and Roux-en-Y anastomosis by taurocholic acid or a mixture of taurocholic and glycocholic acid. However, the incidence of stress ulcers is significantly reduced by adding lysolecithin to the drinking solution containing these bile acids in the same concentration, though lysolecithin alone induces significantly more stress ulcers than tap water in rats with the same operation submitted to immobilisation stress.