The aim of this study was to compare the efficacy of the sodium alginate preparation, Gaviscon Advance, with placebo in the relief of symptoms of reflux oesophagitis. This was a randomised, double-blind, parallel-group, multicentre study conducted at 13 GP centres in the UK. Patients aged between 18 and 70 years, who had experienced symptoms of reflux oesophagitis within the previous 24 h, and on two other occasions within the previous week, were recruited into the study. Patients were evaluated at baseline, and then reassessed after two and four weeks of treatment with sodium alginate or placebo, for symptoms of reflux oesophagitis in the previous 24 h. Patients were required to fill out a diary card twice daily, from which frequency and severity of symptoms were assessed, and the percentage of symptom-free days and nights calculated. Of the 100 patients recruited into the study, 98 received medication (safety population; placebo, n = 50; sodium alginate, n = 48) and 94 were eligible for inclusion in the intention-to-treat (ITT) population (placebo, n = 48; sodium alginate, n = 46). For this population, sodium alginate was assessed as significantly superior by both investigators and patients at week two (p < 0.001 and p = 0.004, respectively) and at week four (p = 0.001 and p < 0.001, respectively). Significantly more patients in the safety population on placebo withdrew from the study (40%) compared with sodium alginate (21%; p = 0.04), due primarily to lack of effect and adverse events. The sodium alginate preparation demonstrated a superior efficacy compared with placebo, which was achieved in a more acceptable volume of medication than a previous standard preparation, Liquid Gaviscon. The reduced dosage volume of the 'new' preparation (Gaviscon Advance) may be expected to improve patient compliance, and thereby increase treatment efficacy.