The effect on stimulated gastric secretion of ingestion of a gelatin capsule containing 127 .mu.g of 16,16-dimethyl prostaglandin [PG] E2 (DM-PG E2) or a liquid containing 127 .mu.g of DM-PG E2 was studied. DM-PG E2 significantly reduced the volume, acid concentration and total acid output of gastric secretion. Secretory inhibition during the 3 h after treatment with the capsule was 37% (volume), 39% (acid concentration) and 60% (acid output). The DM-PG E2 capsule was nearly as effective as an equivalent amount of DM-PG E2 in solution. PG analogues, because of their oral effectiveness and duration of action, may have therapeutic value in peptic ulcer disease.