The effect of Mucaine and Aludrox on basal and food stimulated immunoreactive gastrin has been assessed in normal control subjects and patients with duodenal or gastric ulcer. No differences in gastrin responses were observed either in the basal period or after the protein meal with the two antacids. As previously described, release of gastrin was greatest in gastric ulcer patients but in contrast to previous results,normal subjects seemed to show a greater response than duodenal ulcer patients but this was not statistically significant. Thus the combination of a local anaesthetic oxethazaine with aluminium hydroxide gel does not lead to diminished gastrin release and is not the prime mechanism of action of this agent.