The paper presents the influence of the ranitidine-dextran conjugate on the gastric secretion stimulated with carbachol on rats with a ligated pylorus [correction of ligaturated pilor]. The gastric lesions, the gastric juice volume and the total acidity at 6, 24 and 48 hours after the treatment were examined. Ranitidine serum content was determined by HPLC. Administration of the ranitidine-dextran conjugate produces a higher inhibition of gastric lesions at 48 hours than the administration of the free drug (61.4% versus 33.9%) and a prolonged action for more 48 hours. Synthesis of a macromolecular prodrug of ranitidine and its in vitro behavior was reported in a previous paper (11). The present paper studies the performances obtained in gastro-protective action by using the new ranitidine-dextran conjugate reported (11).