The effect of a sulfated polysaccharide (SN-263) inhibitor of gastric pepsin on the healing rate of gastric ulcer was studied by inpatient double blind and sequential trials. Healing rate was determined from changes in the surface area of ulcers estimated by serial radiography. Ten patients treated with SN-263 in the double blind trial had a mean decrease in ulcer size of 9.14 mm2 per day while nine ulcers in control patients had a mean decrease of 2.21 mm2 per day (P