['Acid secretion inhibitors are of dubious value to most patients with functional dyspepsia but might be effective in a subset. The aims of the trial were to compare the effect of ranitidine with that of placebo in selected subsets of patients.', "Two hundred and twenty-six patients with functional dyspepsia were included in a double-blind multi-crossover (MCO) trial. After 6 weeks an effect score (Xs) with a range of 0-5 was calculated. They were then stratified in accordance with their score and randomized to 4 weeks' double-blind treatment with ranitidine or placebo. Overall symptoms were scored on a 100-mm visual analogue scale, and the change in score (measured in millimetres) was the primary effect measure.", "Two hundred and six patients completed the study. The effect of ranitidine and placebo in the 'responders' (76 patients with Xs of 4-5 after the MCO period) was 28 mm and 5 mm, respectively (P < 0.001), and in all patients 19 mm and 12 mm, respectively (P < 0.03). No effect was seen in 'nonresponders' (130 patients with Xs of 0-3 after the MCO period). The clinical improvement, as judged by the patients given ranitidine during the last 4-week period was statistically significantly different in favour of responders compared with nonresponders. We were unable to characterize the responders on the basis of demographics, symptoms, and signs."] Does ranitidine effectively relieve symptoms in a subset of patients with functional dyspepsia?