AbstractIt is a well known fact that orally administered acetylsalicylic acid causes a high incidence of gastric side effects (from mild gastritis to ulcer). The mechanism for the development of the side effects is still a matter of dispute. In the present study rats were operated and chronic gastric fistulas were performed. This permitted regular collection of gastric juice. The test compound was administered directly into the stomach as pure acetylsalicylic acid or in enteric coated preparation (Premaspin®) which only permitted liberation of the active principle in the alcaline milieu of the duodenum. In addition, deposition of the drug was also made through a tube into the duodenum. The gastric juice was analysed for its variations in HCl concentration. Similar determination of total and free sialic acid was taken as an indication of changes or destruction of the mucoid component. If the drug was liberated in the duodenum or directly placed there or if a small amount of the pure acetylsalicylic acid wa...