Twenty-seven patients with symptomatic gastro-oesophageal reflux received cimetidine 1.6 g daily for 6 weeks and matching placebo for 6 weeks in a randomised double-blind crossover trial. They complained of significantly more episodes of pain on placebo than on cimetidine (1186 vs 581) and consumed significantly more antacid tablets on placebo than on cimetidine (1645 vs. 1011). Cimetidine and placebo had similar effects on mucosal sensitivity to acid and on oesophagitis assessed endoscopically and histologically, suggesting that the symptomatic benefit is the result of a simple antacid effect.