Thirty-six duodenal ulcer patients participated in a randomized controlled trial of the immediate effect of a liquid antacid preparation (Link) and placebo on epigastric pain. The patients recorded the effect of a total of 143 doses of antacid and 148 doses of placebo. Marked or complete relief of pain 30 min after ingestion was found after 62% of the antacid doses and after 52% of the placebo doses. The average effect of antacid was better than the effect of placebo in 21 patients, worse in 8 and equal in 7 patients. This difference in favour of antacid is statistical significant (p less than 0.05) and therefore it is concluded that antacid is more effective than placebo in relieving epigastric pain in duodenal ulcer patients, although the therapeutic gain is small.